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 $206.97   9.518%   $226.6694   $226.67   $226.65   $226.70  
  Purchase #2 $170.47   3.459%   $176.3666   $176.37   $176.35   $176.40  
  Purchase #3 $11.32   6.762%   $12.0855   $12.09   $12.10   $12.10  
  Purchase #4 $77.41   10.385%   $85.449   $85.45   $85.45   $85.40  
  Purchase #5 $12.48   13.177%   $14.1245   $14.12   $14.10   $14.10  
  Purchase #6 $119.72   12.228%   $134.3594   $134.36   $134.35   $134.40  
  Purchase #7 $172.74   7.689%   $186.022   $186.02   $186.00   $186.00  
  7 purchase totals = $771.11       $835.0764   $835.08   $835.00   $835.10