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 $63.36   5.361%   $66.7567   $66.76   $66.75   $66.80  
  Purchase #2 $206.99   8.378%   $224.3316   $224.33   $224.35   $224.30  
  Purchase #3 $171.51   4.834%   $179.8008   $179.80   $179.80   $179.80  
  Purchase #4 $230.37   3.654%   $238.7877   $238.79   $238.80   $238.80  
  Purchase #5 $247.35   13.374%   $280.4306   $280.43   $280.45   $280.40  
  Purchase #6 $208.96   10.132%   $230.1318   $230.13   $230.15   $230.10  
  Purchase #7 $81.32   12.484%   $91.472   $91.47   $91.45   $91.50  
  7 purchase totals = $1,209.86       $1,311.7112   $1,311.71   $1,311.75   $1,311.70