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 $245.87   7.189%   $263.5456   $263.55   $263.55   $263.50  
  Purchase #2 $243.53   12.390%   $273.7034   $273.70   $273.70   $273.70  
  Purchase #3 $230.76   5.498%   $243.4472   $243.45   $243.45   $243.40  
  Purchase #4 $46.32   9.681%   $50.8042   $50.80   $50.80   $50.80  
  Purchase #5 $73.64   4.346%   $76.8404   $76.84   $76.85   $76.80  
  Purchase #6 $60.27   3.597%   $62.4379   $62.44   $62.45   $62.40  
  Purchase #7 $60.79   5.363%   $64.0502   $64.05   $64.05   $64.10  
  7 purchase totals = $961.18       $1,034.8289   $1,034.83   $1,034.85   $1,034.70