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 $53.92   8.486%   $58.4957   $58.50   $58.50   $58.50  
  Purchase #2 $92.48   8.155%   $100.0217   $100.02   $100.00   $100.00  
  Purchase #3 $6.72   10.413%   $7.4198   $7.42   $7.40   $7.40  
  Purchase #4 $63.66   13.326%   $72.1433   $72.14   $72.15   $72.10  
  Purchase #5 $211.29   7.829%   $227.8319   $227.83   $227.85   $227.80  
  Purchase #6 $247.94   10.580%   $274.1721   $274.17   $274.15   $274.20  
  Purchase #7 $22.40   8.151%   $24.2258   $24.23   $24.25   $24.20  
  7 purchase totals = $698.41       $764.3103   $764.31   $764.30   $764.20