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 $164.34   7.819%   $177.1897   $177.19   $177.20   $177.20  
  Purchase #2 $161.47   13.334%   $183.0004   $183.00   $183.00   $183.00  
  Purchase #3 $55.40   7.657%   $59.642   $59.64   $59.65   $59.60  
  Purchase #4 $192.62   11.847%   $215.4397   $215.44   $215.45   $215.40  
  Purchase #5 $121.90   12.638%   $137.3057   $137.31   $137.30   $137.30  
  Purchase #6 $236.73   12.410%   $266.1082   $266.11   $266.10   $266.10  
  Purchase #7 $16.88   11.309%   $18.789   $18.79   $18.80   $18.80  
  7 purchase totals = $949.34       $1,057.4747   $1,057.48   $1,057.50   $1,057.40