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 $207.54   11.719%   $231.8616   $231.86   $231.85   $231.90  
  Purchase #2 $88.80   3.236%   $91.6736   $91.67   $91.65   $91.70  
  Purchase #3 $100.59   7.234%   $107.8667   $107.87   $107.85   $107.90  
  Purchase #4 $213.78   5.755%   $226.083   $226.08   $226.10   $226.10  
  Purchase #5 $229.31   13.852%   $261.074   $261.07   $261.05   $261.10  
  Purchase #6 $90.92   12.486%   $102.2723   $102.27   $102.25   $102.30  
  Purchase #7 $87.53   12.843%   $98.7715   $98.77   $98.75   $98.80  
  7 purchase totals = $1,018.47       $1,119.6027   $1,119.59   $1,119.50   $1,119.80