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 $87.36   6.139%   $92.723   $92.72   $92.70   $92.70  
  Purchase #2 $174.78   5.322%   $184.0818   $184.08   $184.10   $184.10  
  Purchase #3 $48.91   9.636%   $53.623   $53.62   $53.60   $53.60  
  Purchase #4 $67.95   7.326%   $72.928   $72.93   $72.95   $72.90  
  Purchase #5 $188.79   13.116%   $213.5517   $213.55   $213.55   $213.60  
  Purchase #6 $19.85   4.536%   $20.7504   $20.75   $20.75   $20.80  
  Purchase #7 $189.43   5.568%   $199.9775   $199.98   $200.00   $200.00  
  7 purchase totals = $777.07       $837.6354   $837.63   $837.65   $837.70