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 $224.69   9.818%   $246.7501   $246.75   $246.75   $246.80  
  Purchase #2 $206.88   12.391%   $232.5145   $232.51   $232.50   $232.50  
  Purchase #3 $17.75   9.129%   $19.3704   $19.37   $19.35   $19.40  
  Purchase #4 $78.68   11.638%   $87.8368   $87.84   $87.85   $87.80  
  Purchase #5 $232.66   6.345%   $247.4223   $247.42   $247.40   $247.40  
  Purchase #6 $7.86   5.189%   $8.2679   $8.27   $8.25   $8.30  
  Purchase #7 $222.47   5.198%   $234.034   $234.03   $234.05   $234.00  
  7 purchase totals = $990.99       $1,076.1960   $1,076.19   $1,076.15   $1,076.20