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 $87.49   7.504%   $94.0552   $94.06   $94.05   $94.10  
  Purchase #2 $214.26   5.314%   $225.6458   $225.65   $225.65   $225.60  
  Purchase #3 $245.40   11.229%   $272.956   $272.96   $272.95   $273.00  
  Purchase #4 $13.62   8.828%   $14.8224   $14.82   $14.80   $14.80  
  Purchase #5 $34.27   6.413%   $36.4677   $36.47   $36.45   $36.50  
  Purchase #6 $26.48   7.207%   $28.3884   $28.39   $28.40   $28.40  
  Purchase #7 $79.66   13.596%   $90.4906   $90.49   $90.50   $90.50  
  7 purchase totals = $701.18       $762.8261   $762.84   $762.80   $762.90