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 $212.53   11.419%   $236.7988   $236.80   $236.80   $236.80  
  Purchase #2 $127.30   10.783%   $141.0268   $141.03   $141.05   $141.00  
  Purchase #3 $17.37   13.764%   $19.7608   $19.76   $19.75   $19.80  
  Purchase #4 $207.67   8.723%   $225.7851   $225.79   $225.80   $225.80  
  Purchase #5 $11.32   3.728%   $11.742   $11.74   $11.75   $11.70  
  Purchase #6 $57.69   3.791%   $59.877   $59.88   $59.90   $59.90  
  Purchase #7 $216.90   4.656%   $226.9989   $227.00   $227.00   $227.00  
  7 purchase totals = $850.78       $921.9894   $922.00   $922.05   $922.00