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 $183.45   9.565%   $200.997   $201.00   $201.00   $201.00  
  Purchase #2 $158.52   11.425%   $176.6309   $176.63   $176.65   $176.60  
  Purchase #3 $204.36   5.616%   $215.8369   $215.84   $215.85   $215.80  
  Purchase #4 $61.34   10.149%   $67.5654   $67.57   $67.55   $67.60  
  Purchase #5 $145.63   4.413%   $152.0567   $152.06   $152.05   $152.10  
  Purchase #6 $109.92   6.528%   $117.0956   $117.10   $117.10   $117.10  
  Purchase #7 $26.85   13.821%   $30.5609   $30.56   $30.55   $30.60  
  7 purchase totals = $890.07       $960.7434   $960.76   $960.75   $960.80