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 $83.80   11.665%   $93.5753   $93.58   $93.60   $93.60  
  Purchase #2 $13.28   10.585%   $14.6857   $14.69   $14.70   $14.70  
  Purchase #3 $68.61   13.200%   $77.6665   $77.67   $77.65   $77.70  
  Purchase #4 $229.81   11.778%   $256.877   $256.88   $256.90   $256.90  
  Purchase #5 $196.87   3.427%   $203.6167   $203.62   $203.60   $203.60  
  Purchase #6 $181.72   3.380%   $187.8621   $187.86   $187.85   $187.90  
  Purchase #7 $111.98   12.111%   $125.5419   $125.54   $125.55   $125.50  
  7 purchase totals = $886.07       $959.8252   $959.84   $959.85   $959.90