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 $211.83   10.481%   $234.0319   $234.03   $234.05   $234.00  
  Purchase #2 $239.93   11.830%   $268.3137   $268.31   $268.30   $268.30  
  Purchase #3 $184.45   11.455%   $205.5787   $205.58   $205.60   $205.60  
  Purchase #4 $153.99   10.397%   $170.0003   $170.00   $170.00   $170.00  
  Purchase #5 $162.87   12.217%   $182.7678   $182.77   $182.75   $182.80  
  Purchase #6 $22.36   8.406%   $24.2396   $24.24   $24.25   $24.20  
  Purchase #7 $15.34   12.612%   $17.2747   $17.27   $17.25   $17.30  
  7 purchase totals = $990.77       $1,102.2067   $1,102.20   $1,102.20   $1,102.20