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 $62.92   9.280%   $68.759   $68.76   $68.75   $68.80  
  Purchase #2 $145.71   6.188%   $154.7265   $154.73   $154.75   $154.70  
  Purchase #3 $32.79   7.315%   $35.1886   $35.19   $35.20   $35.20  
  Purchase #4 $66.30   5.181%   $69.735   $69.74   $69.75   $69.70  
  Purchase #5 $173.78   8.795%   $189.064   $189.06   $189.05   $189.10  
  Purchase #6 $95.82   8.461%   $103.9273   $103.93   $103.95   $103.90  
  Purchase #7 $7.36   13.263%   $8.3362   $8.34   $8.35   $8.30  
  7 purchase totals = $584.68       $629.7366   $629.75   $629.80   $629.70