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 $69.86   5.237%   $73.5186   $73.52   $73.50   $73.50  
  Purchase #2 $58.82   4.858%   $61.6775   $61.68   $61.70   $61.70  
  Purchase #3 $147.39   5.565%   $155.5923   $155.59   $155.60   $155.60  
  Purchase #4 $38.93   11.388%   $43.3633   $43.36   $43.35   $43.40  
  Purchase #5 $58.87   12.764%   $66.3842   $66.38   $66.40   $66.40  
  Purchase #6 $189.99   10.181%   $209.3329   $209.33   $209.35   $209.30  
  Purchase #7 $191.68   6.519%   $204.1756   $204.18   $204.20   $204.20  
  7 purchase totals = $755.54       $814.0444   $814.04   $814.10   $814.10