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 $203.95   13.216%   $230.904   $230.90   $230.90   $230.90  
  Purchase #2 $206.91   9.232%   $226.0119   $226.01   $226.00   $226.00  
  Purchase #3 $147.33   4.161%   $153.4604   $153.46   $153.45   $153.50  
  Purchase #4 $58.55   9.747%   $64.2569   $64.26   $64.25   $64.30  
  Purchase #5 $250.28   7.487%   $269.0185   $269.02   $269.00   $269.00  
  Purchase #6 $247.64   12.445%   $278.4588   $278.46   $278.45   $278.50  
  Purchase #7 $22.36   8.221%   $24.1982   $24.20   $24.20   $24.20  
  7 purchase totals = $1,137.02       $1,246.3087   $1,246.31   $1,246.25   $1,246.40