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 $183.58   10.226%   $202.3529   $202.35   $202.35   $202.40  
  Purchase #2 $223.93   12.667%   $252.2952   $252.30   $252.30   $252.30  
  Purchase #3 $57.44   9.313%   $62.7894   $62.79   $62.80   $62.80  
  Purchase #4 $180.41   11.579%   $201.2997   $201.30   $201.30   $201.30  
  Purchase #5 $190.32   9.635%   $208.6573   $208.66   $208.65   $208.70  
  Purchase #6 $223.30   10.624%   $247.0234   $247.02   $247.00   $247.00  
  Purchase #7 $58.65   4.712%   $61.4136   $61.41   $61.40   $61.40  
  7 purchase totals = $1,117.63       $1,235.8315   $1,235.83   $1,235.80   $1,235.90