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 $194.26   10.826%   $215.2906   $215.29   $215.30   $215.30  
  Purchase #2 $93.91   4.260%   $97.9106   $97.91   $97.90   $97.90  
  Purchase #3 $81.26   7.324%   $87.2115   $87.21   $87.20   $87.20  
  Purchase #4 $226.69   9.499%   $248.2233   $248.22   $248.20   $248.20  
  Purchase #5 $75.59   12.813%   $85.2753   $85.28   $85.30   $85.30  
  Purchase #6 $18.62   7.440%   $20.0053   $20.01   $20.00   $20.00  
  Purchase #7 $8.48   4.641%   $8.8736   $8.87   $8.85   $8.90  
  7 purchase totals = $698.81       $762.7902   $762.79   $762.75   $762.80