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 $153.39   13.612%   $174.2694   $174.27   $174.25   $174.30  
  Purchase #2 $223.49   4.497%   $233.5403   $233.54   $233.55   $233.50  
  Purchase #3 $121.59   12.633%   $136.9505   $136.95   $136.95   $137.00  
  Purchase #4 $138.95   13.281%   $157.4039   $157.40   $157.40   $157.40  
  Purchase #5 $26.92   8.115%   $29.1046   $29.10   $29.10   $29.10  
  Purchase #6 $161.63   11.567%   $180.3257   $180.33   $180.35   $180.30  
  Purchase #7 $231.64   12.410%   $260.3865   $260.39   $260.40   $260.40  
  7 purchase totals = $1,057.61       $1,171.9809   $1,171.98   $1,172.00   $1,172.00