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 $235.93   10.594%   $260.9244   $260.92   $260.90   $260.90  
  Purchase #2 $240.60   13.717%   $273.6031   $273.60   $273.60   $273.60  
  Purchase #3 $116.37   3.479%   $120.4185   $120.42   $120.40   $120.40  
  Purchase #4 $41.76   11.514%   $46.5682   $46.57   $46.55   $46.60  
  Purchase #5 $157.58   11.467%   $175.6497   $175.65   $175.65   $175.60  
  Purchase #6 $163.57   12.117%   $183.3898   $183.39   $183.40   $183.40  
  Purchase #7 $157.94   3.563%   $163.5674   $163.57   $163.55   $163.60  
  7 purchase totals = $1,113.75       $1,224.1211   $1,224.12   $1,224.05   $1,224.10