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 $104.54   13.634%   $118.793   $118.79   $118.80   $118.80  
  Purchase #2 $67.54   8.543%   $73.3099   $73.31   $73.30   $73.30  
  Purchase #3 $71.76   11.135%   $79.7505   $79.75   $79.75   $79.80  
  Purchase #4 $12.34   12.817%   $13.9216   $13.92   $13.90   $13.90  
  Purchase #5 $73.91   6.795%   $78.9322   $78.93   $78.95   $78.90  
  Purchase #6 $24.58   6.587%   $26.1991   $26.20   $26.20   $26.20  
  Purchase #7 $118.37   9.119%   $129.1642   $129.16   $129.15   $129.20  
  7 purchase totals = $473.04       $520.0705   $520.06   $520.05   $520.10