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 $214.45   4.823%   $224.7929   $224.79   $224.80   $224.80  
  Purchase #2 $185.74   6.763%   $198.3016   $198.30   $198.30   $198.30  
  Purchase #3 $64.80   3.201%   $66.8742   $66.87   $66.85   $66.90  
  Purchase #4 $250.88   7.388%   $269.415   $269.42   $269.40   $269.40  
  Purchase #5 $79.61   12.424%   $89.5007   $89.50   $89.50   $89.50  
  Purchase #6 $98.28   9.347%   $107.4662   $107.47   $107.45   $107.50  
  Purchase #7 $223.80   12.268%   $251.2558   $251.26   $251.25   $251.30  
  7 purchase totals = $1,117.56       $1,207.6064   $1,207.61   $1,207.55   $1,207.70