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 $236.98   11.192%   $263.5028   $263.50   $263.50   $263.50  
  Purchase #2 $13.54   7.242%   $14.5206   $14.52   $14.50   $14.50  
  Purchase #3 $25.66   4.375%   $26.7826   $26.78   $26.80   $26.80  
  Purchase #4 $160.30   3.211%   $165.4472   $165.45   $165.45   $165.40  
  Purchase #5 $127.59   8.441%   $138.3599   $138.36   $138.35   $138.40  
  Purchase #6 $188.54   11.307%   $209.8582   $209.86   $209.85   $209.90  
  Purchase #7 $213.29   3.674%   $221.1263   $221.13   $221.15   $221.10  
  7 purchase totals = $965.90       $1,039.5976   $1,039.60   $1,039.60   $1,039.60