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 $229.65   7.661%   $247.2435   $247.24   $247.25   $247.20  
  Purchase #2 $186.71   11.313%   $207.8325   $207.83   $207.85   $207.80  
  Purchase #3 $205.75   3.676%   $213.3134   $213.31   $213.30   $213.30  
  Purchase #4 $26.90   7.865%   $29.0157   $29.02   $29.00   $29.00  
  Purchase #5 $146.62   10.402%   $161.8714   $161.87   $161.85   $161.90  
  Purchase #6 $48.53   10.580%   $53.6645   $53.66   $53.65   $53.70  
  Purchase #7 $214.28   5.550%   $226.1725   $226.17   $226.15   $226.20  
  7 purchase totals = $1,058.44       $1,139.1135   $1,139.10   $1,139.05   $1,139.10