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 $206.97   9.494%   $226.6197   $226.62   $226.60   $226.60  
  Purchase #2 $35.72   6.159%   $37.92   $37.92   $37.90   $37.90  
  Purchase #3 $205.96   5.315%   $216.9068   $216.91   $216.90   $216.90  
  Purchase #4 $158.45   12.663%   $178.5145   $178.51   $178.50   $178.50  
  Purchase #5 $169.75   4.469%   $177.3361   $177.34   $177.35   $177.30  
  Purchase #6 $106.52   4.106%   $110.8937   $110.89   $110.90   $110.90  
  Purchase #7 $237.98   12.624%   $268.0226   $268.02   $268.00   $268.00  
  7 purchase totals = $1,121.35       $1,216.2134   $1,216.21   $1,216.15   $1,216.10