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 $220.74   5.861%   $233.6776   $233.68   $233.70   $233.70  
  Purchase #2 $232.84   10.655%   $257.6491   $257.65   $257.65   $257.60  
  Purchase #3 $159.64   13.229%   $180.7588   $180.76   $180.75   $180.80  
  Purchase #4 $66.32   11.656%   $74.0503   $74.05   $74.05   $74.10  
  Purchase #5 $116.97   9.673%   $128.2845   $128.28   $128.30   $128.30  
  Purchase #6 $133.68   7.525%   $143.7394   $143.74   $143.75   $143.70  
  Purchase #7 $162.44   7.213%   $174.1568   $174.16   $174.15   $174.20  
  7 purchase totals = $1,092.63       $1,192.3165   $1,192.32   $1,192.35   $1,192.40