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 $156.77   3.844%   $162.7962   $162.80   $162.80   $162.80  
  Purchase #2 $217.56   8.136%   $235.2607   $235.26   $235.25   $235.30  
  Purchase #3 $140.77   10.385%   $155.389   $155.39   $155.40   $155.40  
  Purchase #4 $57.49   9.130%   $62.7388   $62.74   $62.75   $62.70  
  Purchase #5 $146.56   11.366%   $163.218   $163.22   $163.20   $163.20  
  Purchase #6 $194.67   12.682%   $219.358   $219.36   $219.35   $219.40  
  Purchase #7 $35.30   10.525%   $39.0153   $39.02   $39.00   $39.00  
  7 purchase totals = $949.12       $1,037.7760   $1,037.79   $1,037.75   $1,037.80