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 $80.93   6.201%   $85.9485   $85.95   $85.95   $85.90  
  Purchase #2 $31.93   10.758%   $35.365   $35.37   $35.35   $35.40  
  Purchase #3 $15.58   4.495%   $16.2803   $16.28   $16.30   $16.30  
  Purchase #4 $24.30   6.784%   $25.9485   $25.95   $25.95   $25.90  
  Purchase #5 $189.26   12.543%   $212.9989   $213.00   $213.00   $213.00  
  Purchase #6 $16.66   3.671%   $17.2716   $17.27   $17.25   $17.30  
  Purchase #7 $118.80   3.631%   $123.1136   $123.11   $123.10   $123.10  
  7 purchase totals = $477.46       $516.9264   $516.93   $516.90   $516.90