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 $154.31   5.728%   $163.1489   $163.15   $163.15   $163.10  
  Purchase #2 $112.31   11.738%   $125.4929   $125.49   $125.50   $125.50  
  Purchase #3 $140.89   12.513%   $158.5196   $158.52   $158.50   $158.50  
  Purchase #4 $207.87   5.629%   $219.571   $219.57   $219.55   $219.60  
  Purchase #5 $150.92   12.843%   $170.3027   $170.30   $170.30   $170.30  
  Purchase #6 $235.29   13.337%   $266.6706   $266.67   $266.65   $266.70  
  Purchase #7 $155.88   3.700%   $161.6476   $161.65   $161.65   $161.60  
  7 purchase totals = $1,157.47       $1,265.3533   $1,265.35   $1,265.30   $1,265.30