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 $188.52   10.121%   $207.6001   $207.60   $207.60   $207.60  
  Purchase #2 $111.86   6.341%   $118.953   $118.95   $118.95   $119.00  
  Purchase #3 $183.35   12.480%   $206.2321   $206.23   $206.25   $206.20  
  Purchase #4 $65.28   11.727%   $72.9354   $72.94   $72.95   $72.90  
  Purchase #5 $175.26   9.720%   $192.2953   $192.30   $192.30   $192.30  
  Purchase #6 $225.82   11.426%   $251.6222   $251.62   $251.60   $251.60  
  Purchase #7 $132.34   6.274%   $140.643   $140.64   $140.65   $140.60  
  7 purchase totals = $1,082.43       $1,190.2811   $1,190.28   $1,190.30   $1,190.20