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 $191.60   6.129%   $203.3432   $203.34   $203.35   $203.30  
  Purchase #2 $8.90   6.725%   $9.4985   $9.50   $9.50   $9.50  
  Purchase #3 $100.63   5.628%   $106.2935   $106.29   $106.30   $106.30  
  Purchase #4 $141.33   3.497%   $146.2723   $146.27   $146.25   $146.30  
  Purchase #5 $60.64   3.623%   $62.837   $62.84   $62.85   $62.80  
  Purchase #6 $165.75   8.549%   $179.92   $179.92   $179.90   $179.90  
  Purchase #7 $224.70   9.268%   $245.5252   $245.53   $245.55   $245.50  
  7 purchase totals = $893.55       $953.6897   $953.69   $953.70   $953.60