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 $38.31   8.669%   $41.6311   $41.63   $41.65   $41.60  
  Purchase #2 $32.88   6.268%   $34.9409   $34.94   $34.95   $34.90  
  Purchase #3 $201.95   7.791%   $217.6839   $217.68   $217.70   $217.70  
  Purchase #4 $133.98   9.185%   $146.2861   $146.29   $146.30   $146.30  
  Purchase #5 $24.37   4.407%   $25.444   $25.44   $25.45   $25.40  
  Purchase #6 $206.44   11.453%   $230.0836   $230.08   $230.10   $230.10  
  Purchase #7 $232.31   11.433%   $258.87   $258.87   $258.85   $258.90  
  7 purchase totals = $870.24       $954.9396   $954.93   $955.00   $954.90