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 $110.37   12.190%   $123.8241   $123.82   $123.80   $123.80  
  Purchase #2 $162.94   12.656%   $183.5617   $183.56   $183.55   $183.60  
  Purchase #3 $11.36   9.228%   $12.4083   $12.41   $12.40   $12.40  
  Purchase #4 $219.74   3.247%   $226.875   $226.88   $226.90   $226.90  
  Purchase #5 $221.76   6.578%   $236.3474   $236.35   $236.35   $236.30  
  Purchase #6 $118.36   13.216%   $134.0025   $134.00   $134.00   $134.00  
  Purchase #7 $102.75   4.465%   $107.3378   $107.34   $107.35   $107.30  
  7 purchase totals = $947.28       $1,024.3568   $1,024.36   $1,024.35   $1,024.30