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 $207.98   10.708%   $230.2505   $230.25   $230.25   $230.30  
  Purchase #2 $240.84   11.143%   $267.6768   $267.68   $267.70   $267.70  
  Purchase #3 $24.86   3.578%   $25.7495   $25.75   $25.75   $25.70  
  Purchase #4 $94.91   3.465%   $98.1986   $98.20   $98.20   $98.20  
  Purchase #5 $30.34   4.372%   $31.6665   $31.67   $31.65   $31.70  
  Purchase #6 $145.93   5.781%   $154.3662   $154.37   $154.35   $154.40  
  Purchase #7 $109.51   6.115%   $116.2065   $116.21   $116.20   $116.20  
  7 purchase totals = $854.37       $924.1146   $924.13   $924.10   $924.20