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 $58.54   11.599%   $65.3301   $65.33   $65.35   $65.30  
  Purchase #2 $168.69   9.107%   $184.0526   $184.05   $184.05   $184.10  
  Purchase #3 $158.48   13.696%   $180.1854   $180.19   $180.20   $180.20  
  Purchase #4 $209.83   9.157%   $229.0441   $229.04   $229.05   $229.00  
  Purchase #5 $149.81   4.433%   $156.4511   $156.45   $156.45   $156.50  
  Purchase #6 $203.91   6.142%   $216.4342   $216.43   $216.45   $216.40  
  Purchase #7 $248.81   7.486%   $267.4359   $267.44   $267.45   $267.40  
  7 purchase totals = $1,198.07       $1,298.9334   $1,298.93   $1,299.00   $1,298.90