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 $57.94   12.290%   $65.0608   $65.06   $65.05   $65.10  
  Purchase #2 $166.79   9.664%   $182.9086   $182.91   $182.90   $182.90  
  Purchase #3 $118.46   13.495%   $134.4462   $134.45   $134.45   $134.40  
  Purchase #4 $182.46   7.772%   $196.6408   $196.64   $196.65   $196.60  
  Purchase #5 $90.54   6.748%   $96.6496   $96.65   $96.65   $96.60  
  Purchase #6 $193.31   4.209%   $201.4464   $201.45   $201.45   $201.40  
  Purchase #7 $8.76   12.122%   $9.8219   $9.82   $9.80   $9.80  
  7 purchase totals = $818.26       $886.9743   $886.98   $886.95   $886.80