Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $216.90   8.795%   $235.9764   $235.98   $236.00   $236.00  
  Purchase #2 $124.72   10.637%   $137.9865   $137.99   $138.00   $138.00  
  Purchase #3 $114.83   8.498%   $124.5883   $124.59   $124.60   $124.60  
  Purchase #4 $141.29   5.662%   $149.2898   $149.29   $149.30   $149.30  
  Purchase #5 $209.97   4.586%   $219.5992   $219.60   $219.60   $219.60  
  Purchase #6 $199.98   13.150%   $226.2774   $226.28   $226.30   $226.30  
  Purchase #7 $234.54   9.486%   $256.7885   $256.79   $256.80   $256.80  
  7 purchase totals = $1,242.23       $1,350.5061   $1,350.52   $1,350.60   $1,350.60