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 $220.93   12.454%   $248.4446   $248.44   $248.45   $248.40  
  Purchase #2 $95.57   7.862%   $103.0837   $103.08   $103.10   $103.10  
  Purchase #3 $241.50   4.842%   $253.1934   $253.19   $253.20   $253.20  
  Purchase #4 $25.55   6.721%   $27.2672   $27.27   $27.25   $27.30  
  Purchase #5 $112.92   11.246%   $125.619   $125.62   $125.60   $125.60  
  Purchase #6 $35.31   13.642%   $40.127   $40.13   $40.15   $40.10  
  Purchase #7 $203.25   7.608%   $218.7133   $218.71   $218.70   $218.70  
  7 purchase totals = $935.03       $1,016.4482   $1,016.44   $1,016.45   $1,016.40