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 $61.29   11.122%   $68.1067   $68.11   $68.10   $68.10  
  Purchase #2 $84.49   5.489%   $89.1277   $89.13   $89.15   $89.10  
  Purchase #3 $195.47   3.593%   $202.4932   $202.49   $202.50   $202.50  
  Purchase #4 $225.45   7.770%   $242.9675   $242.97   $242.95   $243.00  
  Purchase #5 $192.40   8.283%   $208.3365   $208.34   $208.35   $208.30  
  Purchase #6 $87.55   6.748%   $93.4579   $93.46   $93.45   $93.50  
  Purchase #7 $15.26   12.707%   $17.1991   $17.20   $17.20   $17.20  
  7 purchase totals = $861.91       $921.6886   $921.70   $921.70   $921.70