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 $103.40   13.748%   $117.6154   $117.62   $117.60   $117.60  
  Purchase #2 $174.42   11.293%   $194.1173   $194.12   $194.10   $194.10  
  Purchase #3 $179.29   4.346%   $187.0819   $187.08   $187.10   $187.10  
  Purchase #4 $172.65   3.757%   $179.1365   $179.14   $179.15   $179.10  
  Purchase #5 $93.80   10.630%   $103.7709   $103.77   $103.75   $103.80  
  Purchase #6 $235.93   8.266%   $255.432   $255.43   $255.45   $255.40  
  Purchase #7 $194.60   12.447%   $218.8219   $218.82   $218.80   $218.80  
  7 purchase totals = $1,154.09       $1,255.9759   $1,255.98   $1,255.95   $1,255.90