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 $52.51   7.786%   $56.5984   $56.60   $56.60   $56.60  
  Purchase #2 $242.61   10.861%   $268.9599   $268.96   $268.95   $269.00  
  Purchase #3 $239.70   13.204%   $271.35   $271.35   $271.35   $271.40  
  Purchase #4 $132.27   5.393%   $139.4033   $139.40   $139.40   $139.40  
  Purchase #5 $70.41   6.292%   $74.8402   $74.84   $74.85   $74.80  
  Purchase #6 $236.84   12.861%   $267.3   $267.30   $267.30   $267.30  
  Purchase #7 $230.51   3.438%   $238.4349   $238.43   $238.45   $238.40  
  7 purchase totals = $1,204.85       $1,316.8867   $1,316.88   $1,316.90   $1,316.90