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 $89.81   9.698%   $98.5198   $98.52   $98.50   $98.50  
  Purchase #2 $250.59   7.168%   $268.5523   $268.55   $268.55   $268.60  
  Purchase #3 $186.73   3.683%   $193.6073   $193.61   $193.60   $193.60  
  Purchase #4 $171.91   7.362%   $184.566   $184.57   $184.55   $184.60  
  Purchase #5 $232.49   10.529%   $256.9689   $256.97   $256.95   $257.00  
  Purchase #6 $86.67   10.237%   $95.5424   $95.54   $95.55   $95.50  
  Purchase #7 $95.43   7.422%   $102.5128   $102.51   $102.50   $102.50  
  7 purchase totals = $1,113.63       $1,200.2695   $1,200.27   $1,200.20   $1,200.30