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 $65.80   8.387%   $71.3186   $71.32   $71.30   $71.30  
  Purchase #2 $72.54   10.311%   $80.0196   $80.02   $80.00   $80.00  
  Purchase #3 $221.77   6.704%   $236.6375   $236.64   $236.65   $236.60  
  Purchase #4 $247.41   10.590%   $273.6107   $273.61   $273.60   $273.60  
  Purchase #5 $217.91   6.514%   $232.1047   $232.10   $232.10   $232.10  
  Purchase #6 $93.41   5.139%   $98.2103   $98.21   $98.20   $98.20  
  Purchase #7 $144.82   12.343%   $162.6951   $162.70   $162.70   $162.70  
  7 purchase totals = $1,063.66       $1,154.5965   $1,154.60   $1,154.55   $1,154.50