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 $40.76   7.508%   $43.8203   $43.82   $43.80   $43.80  
  Purchase #2 $163.53   3.503%   $169.2585   $169.26   $169.25   $169.30  
  Purchase #3 $201.67   11.607%   $225.0778   $225.08   $225.10   $225.10  
  Purchase #4 $176.65   3.357%   $182.5801   $182.58   $182.60   $182.60  
  Purchase #5 $98.37   5.224%   $103.5088   $103.51   $103.50   $103.50  
  Purchase #6 $74.57   13.514%   $84.6474   $84.65   $84.65   $84.60  
  Purchase #7 $225.95   10.696%   $250.1176   $250.12   $250.10   $250.10  
  7 purchase totals = $981.50       $1,059.0105   $1,059.02   $1,059.00   $1,059.00