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 $183.41   5.636%   $193.747   $193.75   $193.75   $193.70  
  Purchase #2 $242.25   5.566%   $255.7336   $255.73   $255.75   $255.70  
  Purchase #3 $140.37   12.452%   $157.8489   $157.85   $157.85   $157.80  
  Purchase #4 $135.63   11.142%   $150.7419   $150.74   $150.75   $150.70  
  Purchase #5 $53.58   11.871%   $59.9405   $59.94   $59.95   $59.90  
  Purchase #6 $135.43   5.270%   $142.5672   $142.57   $142.55   $142.60  
  Purchase #7 $245.93   10.390%   $271.4821   $271.48   $271.50   $271.50  
  7 purchase totals = $1,136.60       $1,232.0612   $1,232.06   $1,232.10   $1,231.90