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 $243.76   8.184%   $263.7093   $263.71   $263.70   $263.70  
  Purchase #2 $71.27   9.280%   $77.8839   $77.88   $77.90   $77.90  
  Purchase #3 $202.79   6.134%   $215.2291   $215.23   $215.25   $215.20  
  Purchase #4 $235.89   6.565%   $251.3762   $251.38   $251.40   $251.40  
  Purchase #5 $197.97   11.380%   $220.499   $220.50   $220.50   $220.50  
  Purchase #6 $76.46   8.721%   $83.1281   $83.13   $83.15   $83.10  
  Purchase #7 $123.92   10.588%   $137.0406   $137.04   $137.05   $137.00  
  7 purchase totals = $1,152.06       $1,248.8662   $1,248.87   $1,248.95   $1,248.80