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 $212.93   12.669%   $239.9061   $239.91   $239.90   $239.90  
  Purchase #2 $215.97   4.508%   $225.7059   $225.71   $225.70   $225.70  
  Purchase #3 $36.51   11.718%   $40.7882   $40.79   $40.80   $40.80  
  Purchase #4 $184.91   10.146%   $203.671   $203.67   $203.65   $203.70  
  Purchase #5 $84.99   11.435%   $94.7086   $94.71   $94.70   $94.70  
  Purchase #6 $242.40   8.187%   $262.2453   $262.25   $262.25   $262.20  
  Purchase #7 $111.27   7.870%   $120.0269   $120.03   $120.05   $120.00  
  7 purchase totals = $1,088.98       $1,187.0520   $1,187.07   $1,187.05   $1,187.00