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 $42.69   4.129%   $44.4527   $44.45   $44.45   $44.50  
  Purchase #2 $200.55   8.172%   $216.9389   $216.94   $216.95   $216.90  
  Purchase #3 $156.68   3.860%   $162.7278   $162.73   $162.75   $162.70  
  Purchase #4 $61.55   13.615%   $69.93   $69.93   $69.95   $69.90  
  Purchase #5 $221.70   4.129%   $230.854   $230.85   $230.85   $230.90  
  Purchase #6 $147.62   11.451%   $164.524   $164.52   $164.50   $164.50  
  Purchase #7 $136.72   6.618%   $145.7681   $145.77   $145.75   $145.80  
  7 purchase totals = $967.51       $1,035.1955   $1,035.19   $1,035.20   $1,035.20