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 $95.25   13.655%   $108.2564   $108.26   $108.25   $108.30  
  Purchase #2 $47.34   8.182%   $51.2134   $51.21   $51.20   $51.20  
  Purchase #3 $190.52   5.390%   $200.789   $200.79   $200.80   $200.80  
  Purchase #4 $233.57   12.307%   $262.3155   $262.32   $262.30   $262.30  
  Purchase #5 $219.83   12.330%   $246.935   $246.94   $246.95   $246.90  
  Purchase #6 $204.53   11.310%   $227.6623   $227.66   $227.65   $227.70  
  Purchase #7 $119.98   9.872%   $131.8244   $131.82   $131.80   $131.80  
  7 purchase totals = $1,111.02       $1,228.9960   $1,229.00   $1,228.95   $1,229.00