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 $23.42   12.339%   $26.3098   $26.31   $26.30   $26.30  
  Purchase #2 $39.41   9.128%   $43.0073   $43.01   $43.00   $43.00  
  Purchase #3 $162.32   6.571%   $172.986   $172.99   $173.00   $173.00  
  Purchase #4 $226.88   10.545%   $250.8045   $250.80   $250.80   $250.80  
  Purchase #5 $126.82   5.765%   $134.1312   $134.13   $134.15   $134.10  
  Purchase #6 $85.36   4.170%   $88.9195   $88.92   $88.90   $88.90  
  Purchase #7 $180.43   11.671%   $201.488   $201.49   $201.50   $201.50  
  7 purchase totals = $844.64       $917.6463   $917.65   $917.65   $917.60