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 $32.91   4.652%   $34.441   $34.44   $34.45   $34.40  
  Purchase #2 $174.73   6.523%   $186.1276   $186.13   $186.15   $186.10  
  Purchase #3 $246.98   8.345%   $267.5905   $267.59   $267.60   $267.60  
  Purchase #4 $222.41   13.766%   $253.027   $253.03   $253.05   $253.00  
  Purchase #5 $46.28   9.561%   $50.7048   $50.70   $50.70   $50.70  
  Purchase #6 $58.66   9.154%   $64.0297   $64.03   $64.05   $64.00  
  Purchase #7 $63.26   10.128%   $69.667   $69.67   $69.65   $69.70  
  7 purchase totals = $845.23       $925.5876   $925.59   $925.65   $925.50