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 $216.98   11.469%   $241.8654   $241.87   $241.85   $241.90  
  Purchase #2 $49.89   8.666%   $54.2135   $54.21   $54.20   $54.20  
  Purchase #3 $59.28   8.108%   $64.0864   $64.09   $64.10   $64.10  
  Purchase #4 $176.41   4.417%   $184.202   $184.20   $184.20   $184.20  
  Purchase #5 $16.61   3.796%   $17.2405   $17.24   $17.25   $17.20  
  Purchase #6 $165.92   4.703%   $173.7232   $173.72   $173.70   $173.70  
  Purchase #7 $250.76   10.654%   $277.476   $277.48   $277.50   $277.50  
  7 purchase totals = $935.85       $1,012.8070   $1,012.81   $1,012.80   $1,012.80