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 $74.89   3.531%   $77.5344   $77.53   $77.55   $77.50  
  Purchase #2 $208.81   11.563%   $232.9547   $232.95   $232.95   $233.00  
  Purchase #3 $96.39   5.583%   $101.7715   $101.77   $101.75   $101.80  
  Purchase #4 $23.56   12.370%   $26.4744   $26.47   $26.45   $26.50  
  Purchase #5 $202.46   4.633%   $211.84   $211.84   $211.85   $211.80  
  Purchase #6 $191.66   12.429%   $215.4814   $215.48   $215.50   $215.50  
  Purchase #7 $39.78   7.386%   $42.7182   $42.72   $42.70   $42.70  
  7 purchase totals = $837.55       $908.7746   $908.76   $908.75   $908.80