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 $58.55   6.410%   $62.3031   $62.30   $62.30   $62.30  
  Purchase #2 $8.26   5.687%   $8.7297   $8.73   $8.75   $8.70  
  Purchase #3 $70.35   10.361%   $77.639   $77.64   $77.65   $77.60  
  Purchase #4 $156.25   8.837%   $170.0578   $170.06   $170.05   $170.10  
  Purchase #5 $10.33   4.153%   $10.759   $10.76   $10.75   $10.80  
  Purchase #6 $96.90   4.433%   $101.1956   $101.20   $101.20   $101.20  
  Purchase #7 $245.93   7.555%   $264.51   $264.51   $264.50   $264.50  
  7 purchase totals = $646.57       $695.1942   $695.20   $695.20   $695.20