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 $50.53   8.525%   $54.8377   $54.84   $54.85   $54.80  
  Purchase #2 $186.25   10.859%   $206.4749   $206.47   $206.45   $206.50  
  Purchase #3 $70.53   4.714%   $73.8548   $73.85   $73.85   $73.90  
  Purchase #4 $25.68   6.448%   $27.3358   $27.34   $27.35   $27.30  
  Purchase #5 $194.77   8.672%   $211.6605   $211.66   $211.65   $211.70  
  Purchase #6 $20.26   5.559%   $21.3863   $21.39   $21.40   $21.40  
  Purchase #7 $5.84   5.580%   $6.1659   $6.17   $6.15   $6.20  
  7 purchase totals = $553.86       $601.7159   $601.72   $601.70   $601.80