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 $81.67   7.164%   $87.5208   $87.52   $87.50   $87.50  
  Purchase #2 $188.58   13.292%   $213.6461   $213.65   $213.65   $213.60  
  Purchase #3 $123.36   11.598%   $137.6673   $137.67   $137.65   $137.70  
  Purchase #4 $15.63   4.771%   $16.3757   $16.38   $16.40   $16.40  
  Purchase #5 $238.32   11.867%   $266.6014   $266.60   $266.60   $266.60  
  Purchase #6 $234.60   4.397%   $244.9154   $244.92   $244.90   $244.90  
  Purchase #7 $150.87   5.559%   $159.2569   $159.26   $159.25   $159.30  
  7 purchase totals = $1,033.03       $1,125.9836   $1,126.00   $1,125.95   $1,126.00