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 $197.33   8.577%   $214.255   $214.26   $214.25   $214.30  
  Purchase #2 $42.47   3.603%   $44.0002   $44.00   $44.00   $44.00  
  Purchase #3 $20.26   11.169%   $22.5228   $22.52   $22.50   $22.50  
  Purchase #4 $92.60   5.735%   $97.9106   $97.91   $97.90   $97.90  
  Purchase #5 $233.37   13.837%   $265.6614   $265.66   $265.65   $265.70  
  Purchase #6 $66.53   12.412%   $74.7877   $74.79   $74.80   $74.80  
  Purchase #7 $74.82   13.764%   $85.1182   $85.12   $85.10   $85.10  
  7 purchase totals = $727.38       $804.2559   $804.26   $804.20   $804.30