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 $80.99   5.799%   $85.6866   $85.69   $85.70   $85.70  
  Purchase #2 $192.94   11.301%   $214.7441   $214.74   $214.75   $214.70  
  Purchase #3 $27.96   5.799%   $29.5814   $29.58   $29.60   $29.60  
  Purchase #4 $235.93   8.421%   $255.7977   $255.80   $255.80   $255.80  
  Purchase #5 $108.50   13.520%   $123.1692   $123.17   $123.15   $123.20  
  Purchase #6 $5.89   11.256%   $6.553   $6.55   $6.55   $6.60  
  Purchase #7 $59.45   12.312%   $66.7695   $66.77   $66.75   $66.80  
  7 purchase totals = $711.66       $782.3015   $782.30   $782.30   $782.40