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 $114.54   4.624%   $119.8363   $119.84   $119.85   $119.80  
  Purchase #2 $8.67   11.840%   $9.6965   $9.70   $9.70   $9.70  
  Purchase #3 $232.51   9.416%   $254.4031   $254.40   $254.40   $254.40  
  Purchase #4 $118.56   3.151%   $122.2958   $122.30   $122.30   $122.30  
  Purchase #5 $197.64   10.231%   $217.8605   $217.86   $217.85   $217.90  
  Purchase #6 $29.37   11.719%   $32.8119   $32.81   $32.80   $32.80  
  Purchase #7 $181.72   12.309%   $204.0879   $204.09   $204.10   $204.10  
  7 purchase totals = $883.01       $960.9920   $961.00   $961.00   $961.00