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 $58.86   6.312%   $62.5752   $62.58   $62.60   $62.60  
  Purchase #2 $108.89   4.301%   $113.5734   $113.57   $113.55   $113.60  
  Purchase #3 $70.95   6.723%   $75.72   $75.72   $75.70   $75.70  
  Purchase #4 $192.86   7.609%   $207.5347   $207.53   $207.55   $207.50  
  Purchase #5 $9.85   6.666%   $10.5066   $10.51   $10.50   $10.50  
  Purchase #6 $18.83   5.257%   $19.8199   $19.82   $19.80   $19.80  
  Purchase #7 $126.47   13.389%   $143.4031   $143.40   $143.40   $143.40  
  7 purchase totals = $586.71       $633.1329   $633.13   $633.10   $633.10