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 $162.94   13.426%   $184.8163   $184.82   $184.80   $184.80  
  Purchase #2 $139.90   3.432%   $144.7014   $144.70   $144.70   $144.70  
  Purchase #3 $125.69   12.731%   $141.6916   $141.69   $141.70   $141.70  
  Purchase #4 $156.38   10.574%   $172.9156   $172.92   $172.90   $172.90  
  Purchase #5 $25.45   4.697%   $26.6454   $26.65   $26.65   $26.60  
  Purchase #6 $178.96   3.372%   $184.9945   $184.99   $185.00   $185.00  
  Purchase #7 $84.26   12.568%   $94.8498   $94.85   $94.85   $94.80  
  7 purchase totals = $873.58       $950.6146   $950.62   $950.60   $950.50