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 $217.66   8.869%   $236.9643   $236.96   $236.95   $237.00  
  Purchase #2 $238.34   9.780%   $261.6497   $261.65   $261.65   $261.60  
  Purchase #3 $58.86   4.159%   $61.308   $61.31   $61.30   $61.30  
  Purchase #4 $9.86   5.585%   $10.4107   $10.41   $10.40   $10.40  
  Purchase #5 $212.82   6.451%   $226.549   $226.55   $226.55   $226.50  
  Purchase #6 $99.80   13.364%   $113.1373   $113.14   $113.15   $113.10  
  Purchase #7 $29.55   3.231%   $30.5048   $30.50   $30.50   $30.50  
  7 purchase totals = $866.89       $940.5238   $940.52   $940.50   $940.40