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 $147.27   12.752%   $166.0499   $166.05   $166.05   $166.00  
  Purchase #2 $209.51   9.634%   $229.6942   $229.69   $229.70   $229.70  
  Purchase #3 $11.77   9.449%   $12.8821   $12.88   $12.90   $12.90  
  Purchase #4 $185.29   5.104%   $194.7472   $194.75   $194.75   $194.70  
  Purchase #5 $80.48   7.309%   $86.3623   $86.36   $86.35   $86.40  
  Purchase #6 $23.40   6.497%   $24.9203   $24.92   $24.90   $24.90  
  Purchase #7 $195.54   7.672%   $210.5418   $210.54   $210.55   $210.50  
  7 purchase totals = $853.26       $925.1978   $925.19   $925.20   $925.10