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 $241.89   13.601%   $274.7895   $274.79   $274.80   $274.80  
  Purchase #2 $26.80   10.374%   $29.5802   $29.58   $29.60   $29.60  
  Purchase #3 $99.56   9.206%   $108.7255   $108.73   $108.75   $108.70  
  Purchase #4 $239.61   4.665%   $250.7878   $250.79   $250.80   $250.80  
  Purchase #5 $67.58   5.441%   $71.257   $71.26   $71.25   $71.30  
  Purchase #6 $189.57   13.243%   $214.6748   $214.67   $214.65   $214.70  
  Purchase #7 $214.83   5.277%   $226.1666   $226.17   $226.15   $226.20  
  7 purchase totals = $1,079.84       $1,175.9814   $1,175.99   $1,176.00   $1,176.10