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 $84.84   13.213%   $96.0499   $96.05   $96.05   $96.00  
  Purchase #2 $248.55   7.401%   $266.9452   $266.95   $266.95   $266.90  
  Purchase #3 $196.66   7.342%   $211.0988   $211.10   $211.10   $211.10  
  Purchase #4 $220.79   3.476%   $228.4647   $228.46   $228.45   $228.50  
  Purchase #5 $16.66   6.461%   $17.7364   $17.74   $17.75   $17.70  
  Purchase #6 $35.65   9.776%   $39.1351   $39.14   $39.15   $39.10  
  Purchase #7 $26.28   13.360%   $29.791   $29.79   $29.80   $29.80  
  7 purchase totals = $829.43       $889.2211   $889.23   $889.25   $889.10