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 $72.70   6.736%   $77.5971   $77.60   $77.60   $77.60  
  Purchase #2 $79.87   4.721%   $83.6407   $83.64   $83.65   $83.60  
  Purchase #3 $91.70   4.755%   $96.0603   $96.06   $96.05   $96.10  
  Purchase #4 $77.42   9.154%   $84.507   $84.51   $84.50   $84.50  
  Purchase #5 $107.76   13.761%   $122.5889   $122.59   $122.60   $122.60  
  Purchase #6 $247.48   7.604%   $266.2984   $266.30   $266.30   $266.30  
  Purchase #7 $165.89   5.283%   $174.654   $174.65   $174.65   $174.70  
  7 purchase totals = $842.82       $905.3464   $905.35   $905.35   $905.40