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 $142.89   13.289%   $161.8787   $161.88   $161.90   $161.90  
  Purchase #2 $68.41   11.577%   $76.3298   $76.33   $76.35   $76.30  
  Purchase #3 $121.60   7.528%   $130.754   $130.75   $130.75   $130.80  
  Purchase #4 $59.58   12.381%   $66.9566   $66.96   $66.95   $67.00  
  Purchase #5 $106.32   4.589%   $111.199   $111.20   $111.20   $111.20  
  Purchase #6 $226.34   4.838%   $237.2903   $237.29   $237.30   $237.30  
  Purchase #7 $134.71   12.418%   $151.4383   $151.44   $151.45   $151.40  
  7 purchase totals = $859.85       $935.8467   $935.85   $935.90   $935.90