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 $208.44   11.170%   $231.7227   $231.72   $231.70   $231.70  
  Purchase #2 $13.71   3.642%   $14.2093   $14.21   $14.20   $14.20  
  Purchase #3 $220.70   5.440%   $232.7061   $232.71   $232.70   $232.70  
  Purchase #4 $25.51   6.233%   $27.1   $27.10   $27.10   $27.10  
  Purchase #5 $44.38   7.391%   $47.6601   $47.66   $47.65   $47.70  
  Purchase #6 $180.31   12.676%   $203.1661   $203.17   $203.15   $203.20  
  Purchase #7 $44.77   8.822%   $48.7196   $48.72   $48.70   $48.70  
  7 purchase totals = $737.82       $805.2839   $805.29   $805.20   $805.30