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 $49.98   12.126%   $56.0406   $56.04   $56.05   $56.00  
  Purchase #2 $233.74   10.288%   $257.7872   $257.79   $257.80   $257.80  
  Purchase #3 $203.84   11.558%   $227.3998   $227.40   $227.40   $227.40  
  Purchase #4 $85.64   12.399%   $96.2585   $96.26   $96.25   $96.30  
  Purchase #5 $46.56   6.517%   $49.5943   $49.59   $49.60   $49.60  
  Purchase #6 $219.52   13.261%   $248.6305   $248.63   $248.65   $248.60  
  Purchase #7 $122.71   11.458%   $136.7701   $136.77   $136.75   $136.80  
  7 purchase totals = $961.99       $1,072.4810   $1,072.48   $1,072.50   $1,072.50