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 $54.95   11.541%   $61.2918   $61.29   $61.30   $61.30  
  Purchase #2 $186.39   13.676%   $211.8807   $211.88   $211.90   $211.90  
  Purchase #3 $161.71   9.596%   $177.2277   $177.23   $177.25   $177.20  
  Purchase #4 $185.25   5.240%   $194.9571   $194.96   $194.95   $195.00  
  Purchase #5 $93.36   6.133%   $99.0858   $99.09   $99.10   $99.10  
  Purchase #6 $250.95   12.243%   $281.6738   $281.67   $281.65   $281.70  
  Purchase #7 $61.83   8.367%   $67.0033   $67.00   $67.00   $67.00  
  7 purchase totals = $994.44       $1,093.1202   $1,093.12   $1,093.15   $1,093.20