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 $52.27   5.265%   $55.022   $55.02   $55.00   $55.00  
  Purchase #2 $121.65   10.854%   $134.8539   $134.85   $134.85   $134.90  
  Purchase #3 $68.28   3.576%   $70.7217   $70.72   $70.70   $70.70  
  Purchase #4 $115.71   7.499%   $124.3871   $124.39   $124.40   $124.40  
  Purchase #5 $179.28   12.442%   $201.586   $201.59   $201.60   $201.60  
  Purchase #6 $90.57   7.114%   $97.0131   $97.01   $97.00   $97.00  
  Purchase #7 $103.68   7.433%   $111.3865   $111.39   $111.40   $111.40  
  7 purchase totals = $731.44       $794.9703   $794.97   $794.95   $795.00