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 $82.38   13.492%   $93.4947   $93.49   $93.50   $93.50  
  Purchase #2 $196.83   3.316%   $203.3569   $203.36   $203.35   $203.40  
  Purchase #3 $25.80   8.538%   $28.0028   $28.00   $28.00   $28.00  
  Purchase #4 $47.67   11.352%   $53.0815   $53.08   $53.10   $53.10  
  Purchase #5 $120.57   5.722%   $127.469   $127.47   $127.45   $127.50  
  Purchase #6 $178.25   9.182%   $194.6169   $194.62   $194.60   $194.60  
  Purchase #7 $7.77   13.493%   $8.8184   $8.82   $8.80   $8.80  
  7 purchase totals = $659.27       $708.8402   $708.84   $708.80   $708.90