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 $219.81   3.243%   $226.9384   $226.94   $226.95   $226.90  
  Purchase #2 $180.66   11.206%   $200.9048   $200.90   $200.90   $200.90  
  Purchase #3 $218.78   3.273%   $225.9407   $225.94   $225.95   $225.90  
  Purchase #4 $22.45   6.792%   $23.9748   $23.97   $23.95   $24.00  
  Purchase #5 $119.82   11.471%   $133.5646   $133.56   $133.55   $133.60  
  Purchase #6 $196.65   7.493%   $211.385   $211.39   $211.40   $211.40  
  Purchase #7 $217.70   13.783%   $247.7056   $247.71   $247.70   $247.70  
  7 purchase totals = $1,175.87       $1,270.4139   $1,270.41   $1,270.40   $1,270.40