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 $187.61   10.703%   $207.6899   $207.69   $207.70   $207.70  
  Purchase #2 $118.85   7.625%   $127.9123   $127.91   $127.90   $127.90  
  Purchase #3 $170.33   7.455%   $183.0281   $183.03   $183.05   $183.00  
  Purchase #4 $147.56   11.569%   $164.6312   $164.63   $164.65   $164.60  
  Purchase #5 $141.27   13.697%   $160.6198   $160.62   $160.60   $160.60  
  Purchase #6 $84.52   5.627%   $89.2759   $89.28   $89.30   $89.30  
  Purchase #7 $16.46   9.327%   $17.9952   $18.00   $18.00   $18.00  
  7 purchase totals = $866.60       $951.1524   $951.16   $951.20   $951.10