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 $208.34   13.846%   $237.1868   $237.19   $237.20   $237.20  
  Purchase #2 $173.91   10.617%   $192.374   $192.37   $192.35   $192.40  
  Purchase #3 $38.40   3.234%   $39.6419   $39.64   $39.65   $39.60  
  Purchase #4 $22.89   12.110%   $25.662   $25.66   $25.65   $25.70  
  Purchase #5 $220.63   5.473%   $232.7051   $232.71   $232.70   $232.70  
  Purchase #6 $85.72   13.663%   $97.4319   $97.43   $97.45   $97.40  
  Purchase #7 $81.31   3.684%   $84.3055   $84.31   $84.30   $84.30  
  7 purchase totals = $831.20       $909.3072   $909.31   $909.30   $909.30