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 $53.79   7.480%   $57.8135   $57.81   $57.80   $57.80  
  Purchase #2 $219.37   3.174%   $226.3328   $226.33   $226.35   $226.30  
  Purchase #3 $215.51   4.295%   $224.7662   $224.77   $224.75   $224.80  
  Purchase #4 $234.88   13.830%   $267.3639   $267.36   $267.35   $267.40  
  Purchase #5 $153.53   7.380%   $164.8605   $164.86   $164.85   $164.90  
  Purchase #6 $105.49   9.782%   $115.809   $115.81   $115.80   $115.80  
  Purchase #7 $199.34   4.731%   $208.7708   $208.77   $208.75   $208.80  
  7 purchase totals = $1,181.91       $1,265.7167   $1,265.71   $1,265.65   $1,265.80