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 $126.64   12.561%   $142.5473   $142.55   $142.55   $142.50  
  Purchase #2 $198.95   3.449%   $205.8118   $205.81   $205.80   $205.80  
  Purchase #3 $215.74   9.392%   $236.0023   $236.00   $236.00   $236.00  
  Purchase #4 $68.56   6.568%   $73.063   $73.06   $73.05   $73.10  
  Purchase #5 $12.87   7.529%   $13.839   $13.84   $13.85   $13.80  
  Purchase #6 $220.99   6.450%   $235.2439   $235.24   $235.25   $235.20  
  Purchase #7 $88.68   13.296%   $100.4709   $100.47   $100.45   $100.50  
  7 purchase totals = $932.43       $1,006.9782   $1,006.97   $1,006.95   $1,006.90