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 $55.39   8.281%   $59.9768   $59.98   $60.00   $60.00  
  Purchase #2 $142.56   7.716%   $153.5599   $153.56   $153.55   $153.60  
  Purchase #3 $71.30   5.449%   $75.1851   $75.19   $75.20   $75.20  
  Purchase #4 $160.97   5.620%   $170.0165   $170.02   $170.00   $170.00  
  Purchase #5 $207.42   8.432%   $224.9097   $224.91   $224.90   $224.90  
  Purchase #6 $73.40   3.404%   $75.8985   $75.90   $75.90   $75.90  
  Purchase #7 $214.29   12.817%   $241.7555   $241.76   $241.75   $241.80  
  7 purchase totals = $925.33       $1,001.3020   $1,001.32   $1,001.30   $1,001.40