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 $108.61   13.864%   $123.6677   $123.67   $123.65   $123.70  
  Purchase #2 $175.50   4.624%   $183.6151   $183.62   $183.60   $183.60  
  Purchase #3 $191.42   7.234%   $205.2673   $205.27   $205.25   $205.30  
  Purchase #4 $225.99   4.687%   $236.5822   $236.58   $236.60   $236.60  
  Purchase #5 $137.52   12.419%   $154.5986   $154.60   $154.60   $154.60  
  Purchase #6 $221.55   8.806%   $241.0597   $241.06   $241.05   $241.10  
  Purchase #7 $197.28   13.223%   $223.3663   $223.37   $223.35   $223.40  
  7 purchase totals = $1,257.87       $1,368.1569   $1,368.17   $1,368.10   $1,368.30