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 $182.54   7.732%   $196.654   $196.65   $196.65   $196.70  
  Purchase #2 $60.70   10.245%   $66.9187   $66.92   $66.90   $66.90  
  Purchase #3 $63.49   11.668%   $70.898   $70.90   $70.90   $70.90  
  Purchase #4 $197.42   9.450%   $216.0762   $216.08   $216.10   $216.10  
  Purchase #5 $162.91   6.325%   $173.2141   $173.21   $173.20   $173.20  
  Purchase #6 $65.45   6.199%   $69.5072   $69.51   $69.50   $69.50  
  Purchase #7 $175.34   10.423%   $193.6157   $193.62   $193.60   $193.60  
  7 purchase totals = $907.85       $986.8839   $986.89   $986.85   $986.90