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 $92.51   11.142%   $102.8175   $102.82   $102.80   $102.80  
  Purchase #2 $24.93   7.792%   $26.8725   $26.87   $26.85   $26.90  
  Purchase #3 $152.96   7.561%   $164.5253   $164.53   $164.55   $164.50  
  Purchase #4 $83.34   11.671%   $93.0666   $93.07   $93.05   $93.10  
  Purchase #5 $108.99   4.594%   $113.997   $114.00   $114.00   $114.00  
  Purchase #6 $234.84   7.599%   $252.6855   $252.69   $252.70   $252.70  
  Purchase #7 $99.80   6.330%   $106.1173   $106.12   $106.10   $106.10  
  7 purchase totals = $797.37       $860.0817   $860.10   $860.05   $860.10