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 $86.33   10.214%   $95.1477   $95.15   $95.15   $95.10  
  Purchase #2 $182.86   10.527%   $202.1097   $202.11   $202.10   $202.10  
  Purchase #3 $136.86   7.123%   $146.6085   $146.61   $146.60   $146.60  
  Purchase #4 $101.92   5.408%   $107.4318   $107.43   $107.45   $107.40  
  Purchase #5 $151.86   8.418%   $164.6436   $164.64   $164.65   $164.60  
  Purchase #6 $29.85   11.505%   $33.2842   $33.28   $33.30   $33.30  
  Purchase #7 $204.64   11.454%   $228.0795   $228.08   $228.10   $228.10  
  7 purchase totals = $894.32       $977.3050   $977.30   $977.35   $977.20