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 $142.51   12.193%   $159.8862   $159.89   $159.90   $159.90  
  Purchase #2 $232.52   13.259%   $263.3498   $263.35   $263.35   $263.30  
  Purchase #3 $93.42   12.826%   $105.402   $105.40   $105.40   $105.40  
  Purchase #4 $236.82   4.788%   $248.1589   $248.16   $248.15   $248.20  
  Purchase #5 $213.74   4.690%   $223.7644   $223.76   $223.75   $223.80  
  Purchase #6 $235.74   6.547%   $251.1739   $251.17   $251.15   $251.20  
  Purchase #7 $67.66   11.123%   $75.1858   $75.19   $75.20   $75.20  
  7 purchase totals = $1,222.41       $1,326.9210   $1,326.92   $1,326.90   $1,327.00