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 $24.49   8.323%   $26.5283   $26.53   $26.55   $26.50  
  Purchase #2 $152.42   9.394%   $166.7383   $166.74   $166.75   $166.70  
  Purchase #3 $78.87   11.818%   $88.1909   $88.19   $88.20   $88.20  
  Purchase #4 $208.71   12.165%   $234.0996   $234.10   $234.10   $234.10  
  Purchase #5 $199.59   11.477%   $222.4969   $222.50   $222.50   $222.50  
  Purchase #6 $56.53   7.697%   $60.8811   $60.88   $60.90   $60.90  
  Purchase #7 $156.99   11.166%   $174.5195   $174.52   $174.50   $174.50  
  7 purchase totals = $877.60       $973.4546   $973.46   $973.50   $973.40