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 $84.46   11.519%   $94.1889   $94.19   $94.20   $94.20  
  Purchase #2 $143.69   6.710%   $153.3316   $153.33   $153.35   $153.30  
  Purchase #3 $44.68   4.472%   $46.6781   $46.68   $46.70   $46.70  
  Purchase #4 $224.29   9.115%   $244.734   $244.73   $244.75   $244.70  
  Purchase #5 $158.43   3.845%   $164.5216   $164.52   $164.50   $164.50  
  Purchase #6 $82.57   5.353%   $86.99   $86.99   $87.00   $87.00  
  Purchase #7 $65.38   9.252%   $71.429   $71.43   $71.45   $71.40  
  7 purchase totals = $803.50       $861.8732   $861.87   $861.95   $861.80