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 $22.86   11.535%   $25.4969   $25.50   $25.50   $25.50  
  Purchase #2 $159.61   11.314%   $177.6683   $177.67   $177.65   $177.70  
  Purchase #3 $120.83   13.155%   $136.7252   $136.73   $136.75   $136.70  
  Purchase #4 $217.76   7.331%   $233.724   $233.72   $233.70   $233.70  
  Purchase #5 $19.79   8.194%   $21.4116   $21.41   $21.40   $21.40  
  Purchase #6 $24.94   5.641%   $26.3469   $26.35   $26.35   $26.30  
  Purchase #7 $104.73   8.696%   $113.8373   $113.84   $113.85   $113.80  
  7 purchase totals = $670.52       $735.2102   $735.22   $735.20   $735.10