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 $244.65   9.561%   $268.041   $268.04   $268.05   $268.00  
  Purchase #2 $23.56   13.337%   $26.7022   $26.70   $26.70   $26.70  
  Purchase #3 $45.53   11.520%   $50.7751   $50.78   $50.80   $50.80  
  Purchase #4 $159.49   3.855%   $165.6383   $165.64   $165.65   $165.60  
  Purchase #5 $225.29   3.231%   $232.5691   $232.57   $232.55   $232.60  
  Purchase #6 $46.63   13.434%   $52.8943   $52.89   $52.90   $52.90  
  Purchase #7 $24.68   3.116%   $25.449   $25.45   $25.45   $25.40  
  7 purchase totals = $769.83       $822.0690   $822.07   $822.10   $822.00