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 $82.66   7.105%   $88.533   $88.53   $88.55   $88.50  
  Purchase #2 $193.85   8.653%   $210.6238   $210.62   $210.60   $210.60  
  Purchase #3 $71.59   4.159%   $74.5674   $74.57   $74.55   $74.60  
  Purchase #4 $114.32   5.751%   $120.8945   $120.89   $120.90   $120.90  
  Purchase #5 $194.81   4.124%   $202.844   $202.84   $202.85   $202.80  
  Purchase #6 $70.64   9.210%   $77.1459   $77.15   $77.15   $77.10  
  Purchase #7 $82.32   9.557%   $90.1873   $90.19   $90.20   $90.20  
  7 purchase totals = $810.19       $864.7959   $864.79   $864.80   $864.70