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 $87.73   10.523%   $96.9618   $96.96   $96.95   $97.00  
  Purchase #2 $25.54   7.852%   $27.5454   $27.55   $27.55   $27.50  
  Purchase #3 $201.75   6.779%   $215.4266   $215.43   $215.45   $215.40  
  Purchase #4 $142.57   10.162%   $157.058   $157.06   $157.05   $157.10  
  Purchase #5 $88.92   4.590%   $93.0014   $93.00   $93.00   $93.00  
  Purchase #6 $163.75   11.684%   $182.8826   $182.88   $182.90   $182.90  
  Purchase #7 $69.33   4.785%   $72.6474   $72.65   $72.65   $72.60  
  7 purchase totals = $779.59       $845.5232   $845.53   $845.55   $845.50