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 $71.92   7.554%   $77.3528   $77.35   $77.35   $77.40  
  Purchase #2 $220.70   8.158%   $238.7047   $238.70   $238.70   $238.70  
  Purchase #3 $76.93   9.455%   $84.2037   $84.20   $84.20   $84.20  
  Purchase #4 $137.77   11.344%   $153.3986   $153.40   $153.40   $153.40  
  Purchase #5 $186.75   12.688%   $210.4448   $210.44   $210.45   $210.40  
  Purchase #6 $236.73   4.394%   $247.1319   $247.13   $247.15   $247.10  
  Purchase #7 $57.85   13.586%   $65.7095   $65.71   $65.70   $65.70  
  7 purchase totals = $988.65       $1,076.9460   $1,076.93   $1,076.95   $1,076.90