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 $34.58   6.378%   $36.7855   $36.79   $36.80   $36.80  
  Purchase #2 $188.72   6.322%   $200.6509   $200.65   $200.65   $200.70  
  Purchase #3 $198.56   8.443%   $215.3244   $215.32   $215.30   $215.30  
  Purchase #4 $209.49   4.697%   $219.3297   $219.33   $219.35   $219.30  
  Purchase #5 $146.39   7.789%   $157.7923   $157.79   $157.80   $157.80  
  Purchase #6 $85.37   7.782%   $92.0135   $92.01   $92.00   $92.00  
  Purchase #7 $32.74   3.229%   $33.7972   $33.80   $33.80   $33.80  
  7 purchase totals = $895.85       $955.6935   $955.69   $955.70   $955.70