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 $61.60   3.283%   $63.6223   $63.62   $63.60   $63.60  
  Purchase #2 $241.77   12.416%   $271.7882   $271.79   $271.80   $271.80  
  Purchase #3 $47.39   12.863%   $53.4858   $53.49   $53.50   $53.50  
  Purchase #4 $102.42   4.409%   $106.9357   $106.94   $106.95   $106.90  
  Purchase #5 $217.38   8.158%   $235.1139   $235.11   $235.10   $235.10  
  Purchase #6 $9.35   6.417%   $9.95   $9.95   $9.95   $10.00  
  Purchase #7 $247.58   6.140%   $262.7814   $262.78   $262.80   $262.80  
  7 purchase totals = $927.49       $1,003.6773   $1,003.68   $1,003.70   $1,003.70