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 $138.66   12.839%   $156.4626   $156.46   $156.45   $156.50  
  Purchase #2 $95.86   6.290%   $101.8896   $101.89   $101.90   $101.90  
  Purchase #3 $193.67   4.792%   $202.9507   $202.95   $202.95   $203.00  
  Purchase #4 $88.75   13.278%   $100.5342   $100.53   $100.55   $100.50  
  Purchase #5 $230.54   12.290%   $258.8734   $258.87   $258.85   $258.90  
  Purchase #6 $31.90   7.821%   $34.3949   $34.39   $34.40   $34.40  
  Purchase #7 $189.94   6.178%   $201.6745   $201.67   $201.65   $201.70  
  7 purchase totals = $969.32       $1,056.7799   $1,056.76   $1,056.75   $1,056.90