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 $86.44   11.294%   $96.2025   $96.20   $96.20   $96.20  
  Purchase #2 $137.55   6.318%   $146.2404   $146.24   $146.25   $146.20  
  Purchase #3 $138.27   8.596%   $150.1557   $150.16   $150.15   $150.20  
  Purchase #4 $30.33   9.668%   $33.2623   $33.26   $33.25   $33.30  
  Purchase #5 $69.97   10.148%   $77.0706   $77.07   $77.05   $77.10  
  Purchase #6 $5.97   3.769%   $6.195   $6.20   $6.20   $6.20  
  Purchase #7 $226.96   12.872%   $256.1743   $256.17   $256.15   $256.20  
  7 purchase totals = $695.49       $765.3008   $765.30   $765.25   $765.40