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 $215.90   12.373%   $242.6133   $242.61   $242.60   $242.60  
  Purchase #2 $36.49   13.255%   $41.3267   $41.33   $41.35   $41.30  
  Purchase #3 $107.91   3.558%   $111.7494   $111.75   $111.75   $111.70  
  Purchase #4 $189.46   8.488%   $205.5414   $205.54   $205.55   $205.50  
  Purchase #5 $207.89   3.308%   $214.767   $214.77   $214.75   $214.80  
  Purchase #6 $150.51   12.505%   $169.3313   $169.33   $169.35   $169.30  
  Purchase #7 $213.81   6.783%   $228.3127   $228.31   $228.30   $228.30  
  7 purchase totals = $1,121.97       $1,213.6418   $1,213.64   $1,213.65   $1,213.50