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 $30.94   12.243%   $34.728   $34.73   $34.75   $34.70  
  Purchase #2 $173.58   13.393%   $196.8276   $196.83   $196.85   $196.80  
  Purchase #3 $23.91   10.404%   $26.3976   $26.40   $26.40   $26.40  
  Purchase #4 $31.47   4.733%   $32.9595   $32.96   $32.95   $33.00  
  Purchase #5 $235.25   6.633%   $250.8541   $250.85   $250.85   $250.90  
  Purchase #6 $100.99   5.802%   $106.8494   $106.85   $106.85   $106.80  
  Purchase #7 $106.56   10.264%   $117.4973   $117.50   $117.50   $117.50  
  7 purchase totals = $702.70       $766.1135   $766.12   $766.15   $766.10