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 $112.78   12.676%   $127.076   $127.08   $127.10   $127.10  
  Purchase #2 $65.93   4.535%   $68.9199   $68.92   $68.90   $68.90  
  Purchase #3 $222.87   5.258%   $234.5885   $234.59   $234.60   $234.60  
  Purchase #4 $78.89   8.813%   $85.8426   $85.84   $85.85   $85.80  
  Purchase #5 $182.87   9.421%   $200.0982   $200.10   $200.10   $200.10  
  Purchase #6 $41.97   10.215%   $46.2572   $46.26   $46.25   $46.30  
  Purchase #7 $173.77   7.861%   $187.4301   $187.43   $187.45   $187.40  
  7 purchase totals = $879.08       $950.2125   $950.22   $950.25   $950.20