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 $8.34   12.367%   $9.3714   $9.37   $9.35   $9.40  
  Purchase #2 $52.40   5.686%   $55.3795   $55.38   $55.40   $55.40  
  Purchase #3 $8.75   7.554%   $9.411   $9.41   $9.40   $9.40  
  Purchase #4 $248.49   9.484%   $272.0568   $272.06   $272.05   $272.10  
  Purchase #5 $235.29   11.869%   $263.2166   $263.22   $263.20   $263.20  
  Purchase #6 $135.30   12.519%   $152.2382   $152.24   $152.25   $152.20  
  Purchase #7 $224.32   3.326%   $231.7809   $231.78   $231.80   $231.80  
  7 purchase totals = $912.89       $993.4544   $993.46   $993.45   $993.50