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 $133.58   13.823%   $152.0448   $152.04   $152.05   $152.00  
  Purchase #2 $96.71   4.765%   $101.3182   $101.32   $101.30   $101.30  
  Purchase #3 $196.39   12.331%   $220.6069   $220.61   $220.60   $220.60  
  Purchase #4 $184.73   10.185%   $203.5448   $203.54   $203.55   $203.50  
  Purchase #5 $171.91   7.597%   $184.97   $184.97   $184.95   $185.00  
  Purchase #6 $172.91   11.603%   $192.9727   $192.97   $192.95   $193.00  
  Purchase #7 $249.67   7.711%   $268.9221   $268.92   $268.90   $268.90  
  7 purchase totals = $1,205.90       $1,324.3795   $1,324.37   $1,324.30   $1,324.30