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 $33.75   11.462%   $37.6184   $37.62   $37.60   $37.60  
  Purchase #2 $213.84   13.436%   $242.5715   $242.57   $242.55   $242.60  
  Purchase #3 $162.88   5.506%   $171.8482   $171.85   $171.85   $171.80  
  Purchase #4 $155.91   5.389%   $164.312   $164.31   $164.30   $164.30  
  Purchase #5 $243.29   10.787%   $269.5337   $269.53   $269.55   $269.50  
  Purchase #6 $14.57   7.699%   $15.6917   $15.69   $15.70   $15.70  
  Purchase #7 $168.49   5.171%   $177.2026   $177.20   $177.20   $177.20  
  7 purchase totals = $992.73       $1,078.7781   $1,078.77   $1,078.75   $1,078.70