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 $54.36   13.411%   $61.6502   $61.65   $61.65   $61.70  
  Purchase #2 $28.26   13.375%   $32.0398   $32.04   $32.05   $32.00  
  Purchase #3 $151.59   9.307%   $165.6985   $165.70   $165.70   $165.70  
  Purchase #4 $118.92   10.267%   $131.1295   $131.13   $131.15   $131.10  
  Purchase #5 $75.97   5.159%   $79.8893   $79.89   $79.90   $79.90  
  Purchase #6 $183.61   7.403%   $197.2026   $197.20   $197.20   $197.20  
  Purchase #7 $130.27   4.199%   $135.74   $135.74   $135.75   $135.70  
  7 purchase totals = $742.98       $803.3499   $803.35   $803.40   $803.30