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 $127.39   11.414%   $141.9303   $141.93   $141.95   $141.90  
  Purchase #2 $162.33   13.721%   $184.6033   $184.60   $184.60   $184.60  
  Purchase #3 $236.95   6.779%   $253.0128   $253.01   $253.00   $253.00  
  Purchase #4 $153.99   5.356%   $162.2377   $162.24   $162.25   $162.20  
  Purchase #5 $24.38   6.728%   $26.0203   $26.02   $26.00   $26.00  
  Purchase #6 $242.36   7.811%   $261.2907   $261.29   $261.30   $261.30  
  Purchase #7 $197.60   11.254%   $219.8379   $219.84   $219.85   $219.80  
  7 purchase totals = $1,145.00       $1,248.9330   $1,248.93   $1,248.95   $1,248.80