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 $176.69   13.802%   $201.0768   $201.08   $201.10   $201.10  
  Purchase #2 $88.97   6.248%   $94.5288   $94.53   $94.55   $94.50  
  Purchase #3 $46.38   11.418%   $51.6757   $51.68   $51.70   $51.70  
  Purchase #4 $168.59   9.329%   $184.3178   $184.32   $184.30   $184.30  
  Purchase #5 $23.81   12.797%   $26.857   $26.86   $26.85   $26.90  
  Purchase #6 $134.88   4.515%   $140.9698   $140.97   $140.95   $141.00  
  Purchase #7 $11.69   12.734%   $13.1786   $13.18   $13.20   $13.20  
  7 purchase totals = $651.01       $712.6045   $712.62   $712.65   $712.70