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 $72.73   4.492%   $75.997   $76.00   $76.00   $76.00  
  Purchase #2 $198.89   13.553%   $225.8456   $225.85   $225.85   $225.80  
  Purchase #3 $22.51   11.757%   $25.1565   $25.16   $25.15   $25.20  
  Purchase #4 $225.51   13.647%   $256.2853   $256.29   $256.30   $256.30  
  Purchase #5 $18.79   12.749%   $21.1855   $21.19   $21.20   $21.20  
  Purchase #6 $6.75   4.528%   $7.0556   $7.06   $7.05   $7.10  
  Purchase #7 $153.85   4.247%   $160.384   $160.38   $160.40   $160.40  
  7 purchase totals = $699.03       $771.9095   $771.93   $771.95   $772.00