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 $115.59   8.774%   $125.7319   $125.73   $125.75   $125.70  
  Purchase #2 $247.28   11.717%   $276.2538   $276.25   $276.25   $276.30  
  Purchase #3 $185.84   12.302%   $208.702   $208.70   $208.70   $208.70  
  Purchase #4 $26.29   8.401%   $28.4986   $28.50   $28.50   $28.50  
  Purchase #5 $179.48   3.606%   $185.952   $185.95   $185.95   $186.00  
  Purchase #6 $218.29   12.693%   $245.9975   $246.00   $246.00   $246.00  
  Purchase #7 $26.59   4.666%   $27.8307   $27.83   $27.85   $27.80  
  7 purchase totals = $999.36       $1,098.9665   $1,098.96   $1,099.00   $1,099.00