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 $175.66   12.459%   $197.5455   $197.55   $197.55   $197.50  
  Purchase #2 $6.72   11.405%   $7.4864   $7.49   $7.50   $7.50  
  Purchase #3 $237.59   12.128%   $266.4049   $266.40   $266.40   $266.40  
  Purchase #4 $205.74   13.238%   $232.9759   $232.98   $233.00   $233.00  
  Purchase #5 $200.83   8.167%   $217.2318   $217.23   $217.25   $217.20  
  Purchase #6 $93.88   13.284%   $106.351   $106.35   $106.35   $106.40  
  Purchase #7 $53.92   8.717%   $58.6202   $58.62   $58.60   $58.60  
  7 purchase totals = $974.34       $1,086.6157   $1,086.62   $1,086.65   $1,086.60