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 $36.63   3.461%   $37.8978   $37.90   $37.90   $37.90  
  Purchase #2 $98.49   13.426%   $111.7133   $111.71   $111.70   $111.70  
  Purchase #3 $204.30   10.114%   $224.9629   $224.96   $224.95   $225.00  
  Purchase #4 $52.52   7.471%   $56.4438   $56.44   $56.45   $56.40  
  Purchase #5 $32.99   11.247%   $36.7004   $36.70   $36.70   $36.70  
  Purchase #6 $181.75   3.168%   $187.5078   $187.51   $187.50   $187.50  
  Purchase #7 $53.65   9.527%   $58.7612   $58.76   $58.75   $58.80  
  7 purchase totals = $660.33       $713.9872   $713.98   $713.95   $714.00