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 $50.61   10.696%   $56.0232   $56.02   $56.00   $56.00  
  Purchase #2 $204.38   10.125%   $225.0735   $225.07   $225.05   $225.10  
  Purchase #3 $167.33   6.153%   $177.6258   $177.63   $177.65   $177.60  
  Purchase #4 $170.43   8.516%   $184.9438   $184.94   $184.95   $184.90  
  Purchase #5 $196.34   8.703%   $213.4275   $213.43   $213.45   $213.40  
  Purchase #6 $59.83   11.798%   $66.8887   $66.89   $66.90   $66.90  
  Purchase #7 $91.30   3.260%   $94.2764   $94.28   $94.30   $94.30  
  7 purchase totals = $940.22       $1,018.2589   $1,018.26   $1,018.30   $1,018.20