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 $231.37   13.461%   $262.5147   $262.51   $262.50   $262.50  
  Purchase #2 $141.52   11.797%   $158.2151   $158.22   $158.20   $158.20  
  Purchase #3 $157.26   4.704%   $164.6575   $164.66   $164.65   $164.70  
  Purchase #4 $86.80   3.202%   $89.5793   $89.58   $89.60   $89.60  
  Purchase #5 $161.64   13.204%   $182.9829   $182.98   $183.00   $183.00  
  Purchase #6 $148.71   12.596%   $167.4415   $167.44   $167.45   $167.40  
  Purchase #7 $149.81   12.127%   $167.9775   $167.98   $168.00   $168.00  
  7 purchase totals = $1,077.11       $1,193.3685   $1,193.37   $1,193.40   $1,193.40