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 $34.94   6.738%   $37.2943   $37.29   $37.30   $37.30  
  Purchase #2 $173.95   7.391%   $186.8066   $186.81   $186.80   $186.80  
  Purchase #3 $185.70   13.836%   $211.3935   $211.39   $211.40   $211.40  
  Purchase #4 $232.29   9.204%   $253.67   $253.67   $253.65   $253.70  
  Purchase #5 $146.26   7.181%   $156.7629   $156.76   $156.75   $156.80  
  Purchase #6 $142.81   8.388%   $154.7889   $154.79   $154.80   $154.80  
  Purchase #7 $223.73   4.130%   $232.97   $232.97   $232.95   $233.00  
  7 purchase totals = $1,139.68       $1,233.6862   $1,233.68   $1,233.65   $1,233.80