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 $48.90   10.341%   $53.9567   $53.96   $53.95   $54.00  
  Purchase #2 $49.73   4.187%   $51.8122   $51.81   $51.80   $51.80  
  Purchase #3 $10.97   12.773%   $12.3712   $12.37   $12.35   $12.40  
  Purchase #4 $241.57   10.675%   $267.3576   $267.36   $267.35   $267.40  
  Purchase #5 $209.27   7.237%   $224.4149   $224.41   $224.40   $224.40  
  Purchase #6 $67.51   6.440%   $71.8576   $71.86   $71.85   $71.90  
  Purchase #7 $45.98   6.196%   $48.8289   $48.83   $48.85   $48.80  
  7 purchase totals = $673.93       $730.5991   $730.60   $730.55   $730.70