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 $235.29   5.785%   $248.9015   $248.90   $248.90   $248.90  
  Purchase #2 $229.51   10.353%   $253.2712   $253.27   $253.25   $253.30  
  Purchase #3 $178.51   9.279%   $195.0739   $195.07   $195.05   $195.10  
  Purchase #4 $91.59   5.852%   $96.9498   $96.95   $96.95   $96.90  
  Purchase #5 $113.37   6.755%   $121.0281   $121.03   $121.05   $121.00  
  Purchase #6 $138.35   5.263%   $145.6314   $145.63   $145.65   $145.60  
  Purchase #7 $38.39   10.816%   $42.5423   $42.54   $42.55   $42.50  
  7 purchase totals = $1,025.01       $1,103.3982   $1,103.39   $1,103.40   $1,103.30