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 $226.54   7.598%   $243.7525   $243.75   $243.75   $243.80  
  Purchase #2 $221.50   5.393%   $233.4455   $233.45   $233.45   $233.40  
  Purchase #3 $201.53   11.111%   $223.922   $223.92   $223.90   $223.90  
  Purchase #4 $232.79   13.179%   $263.4694   $263.47   $263.45   $263.50  
  Purchase #5 $137.86   8.616%   $149.738   $149.74   $149.75   $149.70  
  Purchase #6 $229.32   4.646%   $239.9742   $239.97   $239.95   $240.00  
  Purchase #7 $12.31   5.483%   $12.985   $12.99   $13.00   $13.00  
  7 purchase totals = $1,261.85       $1,367.2866   $1,367.29   $1,367.25   $1,367.30