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 $207.43   13.868%   $236.1964   $236.20   $236.20   $236.20  
  Purchase #2 $17.34   8.372%   $18.7917   $18.79   $18.80   $18.80  
  Purchase #3 $57.45   12.459%   $64.6077   $64.61   $64.60   $64.60  
  Purchase #4 $231.58   4.864%   $242.8441   $242.84   $242.85   $242.80  
  Purchase #5 $209.66   9.146%   $228.8355   $228.84   $228.85   $228.80  
  Purchase #6 $183.65   5.323%   $193.4257   $193.43   $193.45   $193.40  
  Purchase #7 $67.77   5.360%   $71.4025   $71.40   $71.40   $71.40  
  7 purchase totals = $974.88       $1,056.1036   $1,056.11   $1,056.15   $1,056.00