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 $241.54   13.205%   $273.4354   $273.44   $273.45   $273.40  
  Purchase #2 $208.61   12.135%   $233.9248   $233.92   $233.90   $233.90  
  Purchase #3 $167.29   10.326%   $184.5644   $184.56   $184.55   $184.60  
  Purchase #4 $192.61   7.681%   $207.4044   $207.40   $207.40   $207.40  
  Purchase #5 $78.38   13.339%   $88.8351   $88.84   $88.85   $88.80  
  Purchase #6 $44.61   4.156%   $46.464   $46.46   $46.45   $46.50  
  Purchase #7 $85.31   6.666%   $90.9968   $91.00   $91.00   $91.00  
  7 purchase totals = $1,018.35       $1,125.6249   $1,125.62   $1,125.60   $1,125.60