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 $228.92   11.567%   $255.3992   $255.40   $255.40   $255.40  
  Purchase #2 $196.35   4.516%   $205.2172   $205.22   $205.20   $205.20  
  Purchase #3 $11.35   11.205%   $12.6218   $12.62   $12.60   $12.60  
  Purchase #4 $166.99   9.399%   $182.6854   $182.69   $182.70   $182.70  
  Purchase #5 $231.83   3.148%   $239.128   $239.13   $239.15   $239.10  
  Purchase #6 $30.97   8.689%   $33.661   $33.66   $33.65   $33.70  
  Purchase #7 $202.67   13.535%   $230.1014   $230.10   $230.10   $230.10  
  7 purchase totals = $1,069.08       $1,158.8140   $1,158.82   $1,158.80   $1,158.80