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 $139.85   5.252%   $147.1949   $147.19   $147.20   $147.20  
  Purchase #2 $243.51   10.726%   $269.6289   $269.63   $269.65   $269.60  
  Purchase #3 $242.30   11.743%   $270.7533   $270.75   $270.75   $270.80  
  Purchase #4 $177.71   8.641%   $193.0659   $193.07   $193.05   $193.10  
  Purchase #5 $209.73   7.850%   $226.1938   $226.19   $226.20   $226.20  
  Purchase #6 $120.86   4.151%   $125.8769   $125.88   $125.90   $125.90  
  Purchase #7 $20.99   12.779%   $23.6723   $23.67   $23.65   $23.70  
  7 purchase totals = $1,154.95       $1,256.3860   $1,256.38   $1,256.40   $1,256.50