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 $67.47   13.116%   $76.3194   $76.32   $76.30   $76.30  
  Purchase #2 $121.37   10.267%   $133.8311   $133.83   $133.85   $133.80  
  Purchase #3 $220.44   7.827%   $237.6938   $237.69   $237.70   $237.70  
  Purchase #4 $153.74   9.192%   $167.8718   $167.87   $167.85   $167.90  
  Purchase #5 $166.88   9.679%   $183.0323   $183.03   $183.05   $183.00  
  Purchase #6 $133.74   5.343%   $140.8857   $140.89   $140.90   $140.90  
  Purchase #7 $249.39   9.270%   $272.5085   $272.51   $272.50   $272.50  
  7 purchase totals = $1,113.03       $1,212.1426   $1,212.14   $1,212.15   $1,212.10