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 $249.58   13.764%   $283.9322   $283.93   $283.95   $283.90  
  Purchase #2 $42.53   5.498%   $44.8683   $44.87   $44.85   $44.90  
  Purchase #3 $204.38   5.472%   $215.5637   $215.56   $215.55   $215.60  
  Purchase #4 $196.71   4.845%   $206.2406   $206.24   $206.25   $206.20  
  Purchase #5 $73.59   9.315%   $80.4449   $80.44   $80.45   $80.40  
  Purchase #6 $248.47   6.707%   $265.1349   $265.13   $265.15   $265.10  
  Purchase #7 $185.99   6.646%   $198.3509   $198.35   $198.35   $198.40  
  7 purchase totals = $1,201.25       $1,294.5355   $1,294.52   $1,294.55   $1,294.50