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 $215.41   13.118%   $243.6675   $243.67   $243.65   $243.70  
  Purchase #2 $206.80   10.724%   $228.9772   $228.98   $229.00   $229.00  
  Purchase #3 $229.37   8.506%   $248.8802   $248.88   $248.90   $248.90  
  Purchase #4 $194.70   12.559%   $219.1524   $219.15   $219.15   $219.20  
  Purchase #5 $22.34   13.653%   $25.3901   $25.39   $25.40   $25.40  
  Purchase #6 $227.33   3.210%   $234.6273   $234.63   $234.65   $234.60  
  Purchase #7 $55.26   13.512%   $62.7267   $62.73   $62.75   $62.70  
  7 purchase totals = $1,151.21       $1,263.4214   $1,263.43   $1,263.50   $1,263.50