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 $69.53   8.793%   $75.6438   $75.64   $75.65   $75.60  
  Purchase #2 $53.67   13.222%   $60.7662   $60.77   $60.75   $60.80  
  Purchase #3 $173.34   11.605%   $193.4561   $193.46   $193.45   $193.50  
  Purchase #4 $103.66   9.203%   $113.1998   $113.20   $113.20   $113.20  
  Purchase #5 $110.74   11.369%   $123.33   $123.33   $123.35   $123.30  
  Purchase #6 $215.45   8.829%   $234.4721   $234.47   $234.45   $234.50  
  Purchase #7 $127.29   7.228%   $136.4905   $136.49   $136.50   $136.50  
  7 purchase totals = $853.68       $937.3585   $937.36   $937.35   $937.40