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 $221.48   10.589%   $244.9325   $244.93   $244.95   $244.90  
  Purchase #2 $156.29   9.815%   $171.6299   $171.63   $171.65   $171.60  
  Purchase #3 $45.71   8.687%   $49.6808   $49.68   $49.70   $49.70  
  Purchase #4 $231.95   8.750%   $252.2456   $252.25   $252.25   $252.20  
  Purchase #5 $193.65   8.153%   $209.4383   $209.44   $209.45   $209.40  
  Purchase #6 $122.32   6.484%   $130.2512   $130.25   $130.25   $130.30  
  Purchase #7 $23.37   11.722%   $26.1094   $26.11   $26.10   $26.10  
  7 purchase totals = $994.77       $1,084.2877   $1,084.29   $1,084.35   $1,084.20