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 $187.34   8.425%   $203.1234   $203.12   $203.10   $203.10  
  Purchase #2 $34.93   13.740%   $39.7294   $39.73   $39.75   $39.70  
  Purchase #3 $163.39   11.749%   $182.5867   $182.59   $182.60   $182.60  
  Purchase #4 $199.78   7.721%   $215.205   $215.21   $215.20   $215.20  
  Purchase #5 $164.73   6.317%   $175.136   $175.14   $175.15   $175.10  
  Purchase #6 $197.85   4.284%   $206.3259   $206.33   $206.35   $206.30  
  Purchase #7 $48.43   13.799%   $55.1129   $55.11   $55.10   $55.10  
  7 purchase totals = $996.45       $1,077.2193   $1,077.23   $1,077.25   $1,077.10