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 $195.46   11.708%   $218.3445   $218.34   $218.35   $218.30  
  Purchase #2 $101.64   10.844%   $112.6618   $112.66   $112.65   $112.70  
  Purchase #3 $204.49   13.867%   $232.8466   $232.85   $232.85   $232.80  
  Purchase #4 $124.92   12.832%   $140.9497   $140.95   $140.95   $140.90  
  Purchase #5 $238.70   6.546%   $254.3253   $254.33   $254.35   $254.30  
  Purchase #6 $33.69   3.862%   $34.9911   $34.99   $35.00   $35.00  
  Purchase #7 $220.34   11.541%   $245.7694   $245.77   $245.75   $245.80  
  7 purchase totals = $1,119.24       $1,239.8884   $1,239.89   $1,239.90   $1,239.80