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 $227.87   13.591%   $258.8398   $258.84   $258.85   $258.80  
  Purchase #2 $178.66   11.522%   $199.2452   $199.25   $199.25   $199.20  
  Purchase #3 $126.52   8.279%   $136.9946   $136.99   $137.00   $137.00  
  Purchase #4 $204.83   4.837%   $214.7376   $214.74   $214.75   $214.70  
  Purchase #5 $59.26   13.864%   $67.4758   $67.48   $67.50   $67.50  
  Purchase #6 $201.71   4.851%   $211.495   $211.50   $211.50   $211.50  
  Purchase #7 $157.84   4.565%   $165.0454   $165.05   $165.05   $165.00  
  7 purchase totals = $1,156.69       $1,253.8334   $1,253.85   $1,253.90   $1,253.70