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 $227.85   8.814%   $247.9327   $247.93   $247.95   $247.90  
  Purchase #2 $226.64   5.819%   $239.8282   $239.83   $239.85   $239.80  
  Purchase #3 $73.82   9.724%   $80.9983   $81.00   $81.00   $81.00  
  Purchase #4 $63.92   5.556%   $67.4714   $67.47   $67.45   $67.50  
  Purchase #5 $15.46   3.582%   $16.0138   $16.01   $16.00   $16.00  
  Purchase #6 $226.26   13.764%   $257.4024   $257.40   $257.40   $257.40  
  Purchase #7 $45.54   12.812%   $51.3746   $51.37   $51.35   $51.40  
  7 purchase totals = $879.49       $961.0214   $961.01   $961.00   $961.00