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 $85.84   13.113%   $97.0962   $97.10   $97.10   $97.10  
  Purchase #2 $92.68   8.164%   $100.2464   $100.25   $100.25   $100.20  
  Purchase #3 $235.33   6.441%   $250.4876   $250.49   $250.50   $250.50  
  Purchase #4 $97.49   11.455%   $108.6575   $108.66   $108.65   $108.70  
  Purchase #5 $156.54   8.705%   $170.1668   $170.17   $170.15   $170.20  
  Purchase #6 $232.82   11.682%   $260.018   $260.02   $260.00   $260.00  
  Purchase #7 $192.79   8.265%   $208.7241   $208.72   $208.70   $208.70  
  7 purchase totals = $1,093.49       $1,195.3966   $1,195.41   $1,195.35   $1,195.40