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 $233.27   8.791%   $253.7768   $253.78   $253.80   $253.80  
  Purchase #2 $98.84   11.304%   $110.0129   $110.01   $110.00   $110.00  
  Purchase #3 $24.35   3.152%   $25.1175   $25.12   $25.10   $25.10  
  Purchase #4 $73.36   8.731%   $79.7651   $79.77   $79.75   $79.80  
  Purchase #5 $92.53   6.277%   $98.3381   $98.34   $98.35   $98.30  
  Purchase #6 $165.51   12.631%   $186.4156   $186.42   $186.40   $186.40  
  Purchase #7 $221.32   3.440%   $228.9334   $228.93   $228.95   $228.90  
  7 purchase totals = $909.18       $982.3594   $982.37   $982.35   $982.30