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 $87.64   12.680%   $98.7528   $98.75   $98.75   $98.80  
  Purchase #2 $6.28   5.678%   $6.6366   $6.64   $6.65   $6.60  
  Purchase #3 $249.68   7.738%   $269.0002   $269.00   $269.00   $269.00  
  Purchase #4 $183.57   5.356%   $193.402   $193.40   $193.40   $193.40  
  Purchase #5 $136.86   3.244%   $141.2997   $141.30   $141.30   $141.30  
  Purchase #6 $158.65   4.107%   $165.1658   $165.17   $165.15   $165.20  
  Purchase #7 $52.66   11.411%   $58.669   $58.67   $58.65   $58.70  
  7 purchase totals = $875.34       $932.9261   $932.93   $932.90   $933.00