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 $88.79   5.199%   $93.4062   $93.41   $93.40   $93.40  
  Purchase #2 $104.42   8.798%   $113.6069   $113.61   $113.60   $113.60  
  Purchase #3 $248.60   6.748%   $265.3755   $265.38   $265.40   $265.40  
  Purchase #4 $178.36   5.865%   $188.8208   $188.82   $188.80   $188.80  
  Purchase #5 $111.98   8.233%   $121.1993   $121.20   $121.20   $121.20  
  Purchase #6 $185.37   4.102%   $192.9739   $192.97   $192.95   $193.00  
  Purchase #7 $96.35   12.728%   $108.6134   $108.61   $108.60   $108.60  
  7 purchase totals = $1,013.87       $1,083.9960   $1,084.00   $1,083.95   $1,084.00