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 $44.57   5.106%   $46.8457   $46.85   $46.85   $46.80  
  Purchase #2 $24.59   4.470%   $25.6892   $25.69   $25.70   $25.70  
  Purchase #3 $83.80   10.347%   $92.4708   $92.47   $92.45   $92.50  
  Purchase #4 $96.59   4.481%   $100.9182   $100.92   $100.90   $100.90  
  Purchase #5 $85.47   11.302%   $95.1298   $95.13   $95.15   $95.10  
  Purchase #6 $195.53   4.322%   $203.9808   $203.98   $204.00   $204.00  
  Purchase #7 $133.32   8.178%   $144.2229   $144.22   $144.20   $144.20  
  7 purchase totals = $663.87       $709.2574   $709.26   $709.25   $709.20