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 $53.83   13.177%   $60.9232   $60.92   $60.90   $60.90  
  Purchase #2 $69.77   10.447%   $77.0589   $77.06   $77.05   $77.10  
  Purchase #3 $74.29   7.275%   $79.6946   $79.69   $79.70   $79.70  
  Purchase #4 $149.93   11.362%   $166.965   $166.97   $166.95   $167.00  
  Purchase #5 $141.29   9.661%   $154.94   $154.94   $154.95   $154.90  
  Purchase #6 $233.90   11.518%   $260.8406   $260.84   $260.85   $260.80  
  Purchase #7 $52.60   10.136%   $57.9315   $57.93   $57.95   $57.90  
  7 purchase totals = $775.61       $858.3538   $858.35   $858.35   $858.30