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 $178.41   5.746%   $188.6614   $188.66   $188.65   $188.70  
  Purchase #2 $161.87   9.380%   $177.0534   $177.05   $177.05   $177.10  
  Purchase #3 $29.84   11.776%   $33.354   $33.35   $33.35   $33.40  
  Purchase #4 $165.49   7.394%   $177.7263   $177.73   $177.75   $177.70  
  Purchase #5 $212.36   5.576%   $224.2012   $224.20   $224.20   $224.20  
  Purchase #6 $217.63   5.540%   $229.6867   $229.69   $229.70   $229.70  
  Purchase #7 $190.68   5.720%   $201.5869   $201.59   $201.60   $201.60  
  7 purchase totals = $1,156.28       $1,232.2699   $1,232.27   $1,232.30   $1,232.40