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 $190.37   8.467%   $206.4886   $206.49   $206.50   $206.50  
  Purchase #2 $248.90   6.331%   $264.6579   $264.66   $264.65   $264.70  
  Purchase #3 $246.40   7.863%   $265.7744   $265.77   $265.75   $265.80  
  Purchase #4 $106.27   9.551%   $116.4198   $116.42   $116.40   $116.40  
  Purchase #5 $203.96   9.319%   $222.967   $222.97   $222.95   $223.00  
  Purchase #6 $87.38   4.388%   $91.2142   $91.21   $91.20   $91.20  
  Purchase #7 $45.94   6.252%   $48.8122   $48.81   $48.80   $48.80  
  7 purchase totals = $1,129.22       $1,216.3341   $1,216.33   $1,216.25   $1,216.40