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 $25.46   4.477%   $26.5998   $26.60   $26.60   $26.60  
  Purchase #2 $144.61   9.399%   $158.2019   $158.20   $158.20   $158.20  
  Purchase #3 $32.42   13.609%   $36.832   $36.83   $36.85   $36.80  
  Purchase #4 $211.31   3.819%   $219.3799   $219.38   $219.40   $219.40  
  Purchase #5 $102.60   9.694%   $112.546   $112.55   $112.55   $112.50  
  Purchase #6 $243.67   12.869%   $275.0279   $275.03   $275.05   $275.00  
  Purchase #7 $104.75   13.163%   $118.5382   $118.54   $118.55   $118.50  
  7 purchase totals = $864.82       $947.1257   $947.13   $947.20   $947.00