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 $33.43   9.663%   $36.6603   $36.66   $36.65   $36.70  
  Purchase #2 $234.45   12.453%   $263.6461   $263.65   $263.65   $263.60  
  Purchase #3 $221.69   4.359%   $231.3535   $231.35   $231.35   $231.40  
  Purchase #4 $245.32   8.457%   $266.0667   $266.07   $266.05   $266.10  
  Purchase #5 $38.90   6.824%   $41.5545   $41.55   $41.55   $41.60  
  Purchase #6 $41.34   11.360%   $46.0362   $46.04   $46.05   $46.00  
  Purchase #7 $95.84   6.405%   $101.9786   $101.98   $102.00   $102.00  
  7 purchase totals = $910.97       $987.2959   $987.30   $987.30   $987.40