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 $236.40   11.111%   $262.6664   $262.67   $262.65   $262.70  
  Purchase #2 $173.93   13.819%   $197.9654   $197.97   $197.95   $198.00  
  Purchase #3 $10.70   4.221%   $11.1516   $11.15   $11.15   $11.20  
  Purchase #4 $51.33   6.259%   $54.5427   $54.54   $54.55   $54.50  
  Purchase #5 $145.50   10.705%   $161.0758   $161.08   $161.10   $161.10  
  Purchase #6 $148.84   9.260%   $162.6226   $162.62   $162.60   $162.60  
  Purchase #7 $45.61   7.266%   $48.924   $48.92   $48.90   $48.90  
  7 purchase totals = $812.31       $898.9485   $898.95   $898.90   $899.00