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 $82.92   10.479%   $91.6092   $91.61   $91.60   $91.60  
  Purchase #2 $24.90   10.628%   $27.5464   $27.55   $27.55   $27.50  
  Purchase #3 $20.73   10.524%   $22.9116   $22.91   $22.90   $22.90  
  Purchase #4 $31.74   13.238%   $35.9417   $35.94   $35.95   $35.90  
  Purchase #5 $113.84   4.861%   $119.3738   $119.37   $119.35   $119.40  
  Purchase #6 $245.42   6.156%   $260.5281   $260.53   $260.55   $260.50  
  Purchase #7 $211.70   12.262%   $237.6587   $237.66   $237.65   $237.70  
  7 purchase totals = $731.25       $795.5695   $795.57   $795.55   $795.50