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 $59.87   3.580%   $62.0133   $62.01   $62.00   $62.00  
  Purchase #2 $126.69   4.523%   $132.4202   $132.42   $132.40   $132.40  
  Purchase #3 $15.57   6.415%   $16.5688   $16.57   $16.55   $16.60  
  Purchase #4 $181.68   13.260%   $205.7708   $205.77   $205.75   $205.80  
  Purchase #5 $73.76   5.471%   $77.7954   $77.80   $77.80   $77.80  
  Purchase #6 $42.63   5.191%   $44.8429   $44.84   $44.85   $44.80  
  Purchase #7 $127.83   3.345%   $132.1059   $132.11   $132.10   $132.10  
  7 purchase totals = $628.03       $671.5173   $671.52   $671.45   $671.50