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 $112.36   11.357%   $125.1207   $125.12   $125.10   $125.10  
  Purchase #2 $134.58   4.662%   $140.8541   $140.85   $140.85   $140.90  
  Purchase #3 $239.69   10.246%   $264.2486   $264.25   $264.25   $264.20  
  Purchase #4 $67.95   4.528%   $71.0268   $71.03   $71.05   $71.00  
  Purchase #5 $184.62   10.415%   $203.8482   $203.85   $203.85   $203.80  
  Purchase #6 $33.84   10.850%   $37.5116   $37.51   $37.50   $37.50  
  Purchase #7 $159.65   12.275%   $179.247   $179.25   $179.25   $179.20  
  7 purchase totals = $932.69       $1,021.8570   $1,021.86   $1,021.85   $1,021.70