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 $162.57   9.736%   $178.3978   $178.40   $178.40   $178.40  
  Purchase #2 $193.93   5.106%   $203.8321   $203.83   $203.85   $203.80  
  Purchase #3 $124.32   3.203%   $128.302   $128.30   $128.30   $128.30  
  Purchase #4 $157.91   6.692%   $168.4773   $168.48   $168.50   $168.50  
  Purchase #5 $93.79   11.154%   $104.2513   $104.25   $104.25   $104.30  
  Purchase #6 $222.48   6.192%   $236.256   $236.26   $236.25   $236.30  
  Purchase #7 $195.67   13.358%   $221.8076   $221.81   $221.80   $221.80  
  7 purchase totals = $1,150.67       $1,241.3241   $1,241.33   $1,241.35   $1,241.40