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 $245.94   5.320%   $259.024   $259.02   $259.00   $259.00  
  Purchase #2 $204.65   13.680%   $232.6461   $232.65   $232.65   $232.60  
  Purchase #3 $145.84   4.639%   $152.6055   $152.61   $152.60   $152.60  
  Purchase #4 $87.68   8.536%   $95.1644   $95.16   $95.15   $95.20  
  Purchase #5 $175.57   4.713%   $183.8446   $183.84   $183.85   $183.80  
  Purchase #6 $70.64   12.660%   $79.583   $79.58   $79.60   $79.60  
  Purchase #7 $248.69   7.103%   $266.3545   $266.35   $266.35   $266.40  
  7 purchase totals = $1,179.01       $1,269.2221   $1,269.21   $1,269.20   $1,269.20