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 $61.91   13.742%   $70.4177   $70.42   $70.40   $70.40  
  Purchase #2 $156.46   6.739%   $167.0038   $167.00   $167.00   $167.00  
  Purchase #3 $124.44   7.736%   $134.0667   $134.07   $134.05   $134.10  
  Purchase #4 $173.99   11.229%   $193.5273   $193.53   $193.55   $193.50  
  Purchase #5 $180.61   11.719%   $201.7757   $201.78   $201.80   $201.80  
  Purchase #6 $123.71   7.641%   $133.1627   $133.16   $133.15   $133.20  
  Purchase #7 $244.96   8.498%   $265.7767   $265.78   $265.80   $265.80  
  7 purchase totals = $1,066.08       $1,165.7306   $1,165.74   $1,165.75   $1,165.80