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 $164.74   6.250%   $175.0363   $175.04   $175.05   $175.00  
  Purchase #2 $109.88   9.547%   $120.3702   $120.37   $120.35   $120.40  
  Purchase #3 $72.26   10.203%   $79.6327   $79.63   $79.65   $79.60  
  Purchase #4 $244.99   4.248%   $255.3972   $255.40   $255.40   $255.40  
  Purchase #5 $132.65   13.657%   $150.766   $150.77   $150.75   $150.80  
  Purchase #6 $98.60   8.822%   $107.2985   $107.30   $107.30   $107.30  
  Purchase #7 $86.68   12.838%   $97.808   $97.81   $97.80   $97.80  
  7 purchase totals = $909.80       $986.3089   $986.32   $986.30   $986.30