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 $210.83   12.248%   $236.6525   $236.65   $236.65   $236.70  
  Purchase #2 $118.39   4.723%   $123.9816   $123.98   $124.00   $124.00  
  Purchase #3 $20.57   13.808%   $23.4103   $23.41   $23.40   $23.40  
  Purchase #4 $26.38   13.410%   $29.9176   $29.92   $29.90   $29.90  
  Purchase #5 $49.79   4.718%   $52.1391   $52.14   $52.15   $52.10  
  Purchase #6 $200.96   12.820%   $226.7231   $226.72   $226.70   $226.70  
  Purchase #7 $88.56   4.661%   $92.6878   $92.69   $92.70   $92.70  
  7 purchase totals = $715.48       $785.5120   $785.51   $785.50   $785.50