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 $227.76   13.252%   $257.9428   $257.94   $257.95   $257.90  
  Purchase #2 $194.54   8.108%   $210.3133   $210.31   $210.30   $210.30  
  Purchase #3 $194.69   6.207%   $206.7744   $206.77   $206.75   $206.80  
  Purchase #4 $170.91   13.228%   $193.518   $193.52   $193.50   $193.50  
  Purchase #5 $37.84   9.427%   $41.4072   $41.41   $41.40   $41.40  
  Purchase #6 $207.52   4.773%   $217.4249   $217.42   $217.40   $217.40  
  Purchase #7 $5.55   7.405%   $5.961   $5.96   $5.95   $6.00  
  7 purchase totals = $1,038.81       $1,133.3416   $1,133.33   $1,133.25   $1,133.30