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 $230.60   10.558%   $254.9467   $254.95   $254.95   $254.90  
  Purchase #2 $33.58   4.520%   $35.0978   $35.10   $35.10   $35.10  
  Purchase #3 $197.55   4.322%   $206.0881   $206.09   $206.10   $206.10  
  Purchase #4 $225.39   12.735%   $254.0934   $254.09   $254.10   $254.10  
  Purchase #5 $144.90   5.344%   $152.6435   $152.64   $152.65   $152.60  
  Purchase #6 $116.74   3.852%   $121.2368   $121.24   $121.25   $121.20  
  Purchase #7 $197.64   10.250%   $217.8981   $217.90   $217.90   $217.90  
  7 purchase totals = $1,146.40       $1,242.0044   $1,242.01   $1,242.05   $1,241.90