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 $95.72   9.314%   $104.6354   $104.64   $104.65   $104.60  
  Purchase #2 $75.44   10.773%   $83.5672   $83.57   $83.55   $83.60  
  Purchase #3 $74.72   12.389%   $83.9771   $83.98   $84.00   $84.00  
  Purchase #4 $246.63   7.465%   $265.0409   $265.04   $265.05   $265.00  
  Purchase #5 $187.94   10.660%   $207.9744   $207.97   $207.95   $208.00  
  Purchase #6 $169.43   8.689%   $184.1518   $184.15   $184.15   $184.20  
  Purchase #7 $211.44   6.758%   $225.7291   $225.73   $225.75   $225.70  
  7 purchase totals = $1,061.32       $1,155.0759   $1,155.08   $1,155.10   $1,155.10