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 $244.62   7.618%   $263.2552   $263.26   $263.25   $263.30  
  Purchase #2 $33.64   9.504%   $36.8371   $36.84   $36.85   $36.80  
  Purchase #3 $193.77   7.689%   $208.669   $208.67   $208.65   $208.70  
  Purchase #4 $32.50   8.699%   $35.3272   $35.33   $35.35   $35.30  
  Purchase #5 $250.77   12.498%   $282.1112   $282.11   $282.10   $282.10  
  Purchase #6 $85.88   11.755%   $95.9752   $95.98   $96.00   $96.00  
  Purchase #7 $200.33   12.533%   $225.4374   $225.44   $225.45   $225.40  
  7 purchase totals = $1,041.51       $1,147.6123   $1,147.63   $1,147.65   $1,147.60