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 $186.76   13.324%   $211.6439   $211.64   $211.65   $211.60  
  Purchase #2 $117.86   9.607%   $129.1828   $129.18   $129.20   $129.20  
  Purchase #3 $162.33   5.658%   $171.5146   $171.51   $171.50   $171.50  
  Purchase #4 $38.81   3.128%   $40.024   $40.02   $40.00   $40.00  
  Purchase #5 $26.62   10.692%   $29.4662   $29.47   $29.45   $29.50  
  Purchase #6 $129.77   3.563%   $134.3937   $134.39   $134.40   $134.40  
  Purchase #7 $104.59   13.325%   $118.5266   $118.53   $118.55   $118.50  
  7 purchase totals = $766.74       $834.7518   $834.74   $834.75   $834.70