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 $111.97   5.488%   $118.1149   $118.11   $118.10   $118.10  
  Purchase #2 $175.81   12.461%   $197.7177   $197.72   $197.70   $197.70  
  Purchase #3 $167.64   9.627%   $183.7787   $183.78   $183.80   $183.80  
  Purchase #4 $89.87   4.581%   $93.9869   $93.99   $94.00   $94.00  
  Purchase #5 $220.38   10.183%   $242.8213   $242.82   $242.80   $242.80  
  Purchase #6 $157.83   13.625%   $179.3343   $179.33   $179.35   $179.30  
  Purchase #7 $60.72   7.819%   $65.4677   $65.47   $65.45   $65.50  
  7 purchase totals = $984.22       $1,081.2215   $1,081.22   $1,081.20   $1,081.20