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 $219.30   3.273%   $226.4777   $226.48   $226.50   $226.50  
  Purchase #2 $86.71   4.773%   $90.8487   $90.85   $90.85   $90.80  
  Purchase #3 $56.76   6.396%   $60.3904   $60.39   $60.40   $60.40  
  Purchase #4 $249.99   6.612%   $266.5193   $266.52   $266.50   $266.50  
  Purchase #5 $178.48   11.432%   $198.8838   $198.88   $198.90   $198.90  
  Purchase #6 $220.51   4.806%   $231.1077   $231.11   $231.10   $231.10  
  Purchase #7 $225.83   3.224%   $233.1108   $233.11   $233.10   $233.10  
  7 purchase totals = $1,237.58       $1,307.3384   $1,307.34   $1,307.35   $1,307.30