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 $192.81   12.207%   $216.3463   $216.35   $216.35   $216.30  
  Purchase #2 $32.52   7.472%   $34.9499   $34.95   $34.95   $34.90  
  Purchase #3 $217.98   4.802%   $228.4474   $228.45   $228.45   $228.40  
  Purchase #4 $204.50   10.817%   $226.6208   $226.62   $226.60   $226.60  
  Purchase #5 $37.42   13.863%   $42.6075   $42.61   $42.60   $42.60  
  Purchase #6 $180.65   10.685%   $199.9525   $199.95   $199.95   $200.00  
  Purchase #7 $56.96   13.721%   $64.7755   $64.78   $64.80   $64.80  
  7 purchase totals = $922.84       $1,013.6999   $1,013.71   $1,013.70   $1,013.60