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 $56.79   8.591%   $61.6688   $61.67   $61.65   $61.70  
  Purchase #2 $104.80   7.548%   $112.7103   $112.71   $112.70   $112.70  
  Purchase #3 $213.60   5.801%   $225.9909   $225.99   $226.00   $226.00  
  Purchase #4 $220.62   8.802%   $240.039   $240.04   $240.05   $240.00  
  Purchase #5 $95.82   12.451%   $107.7505   $107.75   $107.75   $107.80  
  Purchase #6 $123.86   4.541%   $129.4845   $129.48   $129.50   $129.50  
  Purchase #7 $150.32   5.715%   $158.9108   $158.91   $158.90   $158.90  
  7 purchase totals = $965.81       $1,036.5548   $1,036.55   $1,036.55   $1,036.60