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 $182.71   12.582%   $205.6986   $205.70   $205.70   $205.70  
  Purchase #2 $236.25   11.678%   $263.8393   $263.84   $263.85   $263.80  
  Purchase #3 $21.33   6.365%   $22.6877   $22.69   $22.70   $22.70  
  Purchase #4 $195.96   8.173%   $211.9758   $211.98   $212.00   $212.00  
  Purchase #5 $38.29   11.610%   $42.7355   $42.74   $42.75   $42.70  
  Purchase #6 $68.78   5.395%   $72.4907   $72.49   $72.50   $72.50  
  Purchase #7 $184.83   3.566%   $191.421   $191.42   $191.40   $191.40  
  7 purchase totals = $928.15       $1,010.8486   $1,010.86   $1,010.90   $1,010.80