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 $214.87   12.514%   $241.7588   $241.76   $241.75   $241.80  
  Purchase #2 $31.84   10.304%   $35.1208   $35.12   $35.10   $35.10  
  Purchase #3 $146.39   7.634%   $157.5654   $157.57   $157.55   $157.60  
  Purchase #4 $102.30   8.803%   $111.3055   $111.31   $111.30   $111.30  
  Purchase #5 $244.30   5.794%   $258.4547   $258.45   $258.45   $258.50  
  Purchase #6 $231.41   4.494%   $241.8096   $241.81   $241.80   $241.80  
  Purchase #7 $77.53   13.570%   $88.0508   $88.05   $88.05   $88.10  
  7 purchase totals = $1,048.64       $1,134.0656   $1,134.07   $1,134.00   $1,134.20