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 $213.94   6.227%   $227.262   $227.26   $227.25   $227.30  
  Purchase #2 $22.76   11.103%   $25.287   $25.29   $25.30   $25.30  
  Purchase #3 $103.65   10.307%   $114.3332   $114.33   $114.35   $114.30  
  Purchase #4 $124.64   6.597%   $132.8625   $132.86   $132.85   $132.90  
  Purchase #5 $145.99   9.813%   $160.316   $160.32   $160.30   $160.30  
  Purchase #6 $137.86   6.232%   $146.4514   $146.45   $146.45   $146.50  
  Purchase #7 $206.31   3.872%   $214.2983   $214.30   $214.30   $214.30  
  7 purchase totals = $955.15       $1,020.8104   $1,020.81   $1,020.80   $1,020.90