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 $164.31   11.570%   $183.3207   $183.32   $183.30   $183.30  
  Purchase #2 $204.80   10.446%   $226.1934   $226.19   $226.20   $226.20  
  Purchase #3 $73.42   4.758%   $76.9133   $76.91   $76.90   $76.90  
  Purchase #4 $242.58   11.181%   $269.7029   $269.70   $269.70   $269.70  
  Purchase #5 $89.80   12.836%   $101.3267   $101.33   $101.35   $101.30  
  Purchase #6 $136.67   7.600%   $147.0569   $147.06   $147.05   $147.10  
  Purchase #7 $114.48   7.576%   $123.153   $123.15   $123.15   $123.20  
  7 purchase totals = $1,026.06       $1,127.6669   $1,127.66   $1,127.65   $1,127.70