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 $173.90   11.456%   $193.822   $193.82   $193.80   $193.80  
  Purchase #2 $46.56   9.561%   $51.0116   $51.01   $51.00   $51.00  
  Purchase #3 $55.54   12.811%   $62.6552   $62.66   $62.65   $62.70  
  Purchase #4 $69.61   6.325%   $74.0128   $74.01   $74.00   $74.00  
  Purchase #5 $166.61   5.800%   $176.2734   $176.27   $176.25   $176.30  
  Purchase #6 $235.75   13.515%   $267.6116   $267.61   $267.60   $267.60  
  Purchase #7 $119.26   3.577%   $123.5259   $123.53   $123.55   $123.50  
  7 purchase totals = $867.23       $948.9125   $948.91   $948.85   $948.90