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 $120.42   5.183%   $126.6614   $126.66   $126.65   $126.70  
  Purchase #2 $225.59   12.308%   $253.3556   $253.36   $253.35   $253.40  
  Purchase #3 $119.27   11.751%   $133.2854   $133.29   $133.30   $133.30  
  Purchase #4 $69.55   9.417%   $76.0995   $76.10   $76.10   $76.10  
  Purchase #5 $117.85   9.361%   $128.8819   $128.88   $128.90   $128.90  
  Purchase #6 $99.42   7.608%   $106.9839   $106.98   $107.00   $107.00  
  Purchase #7 $244.37   13.873%   $278.2715   $278.27   $278.25   $278.30  
  7 purchase totals = $996.47       $1,103.5392   $1,103.54   $1,103.55   $1,103.70