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 $60.97   3.348%   $63.0113   $63.01   $63.00   $63.00  
  Purchase #2 $186.57   3.718%   $193.5067   $193.51   $193.50   $193.50  
  Purchase #3 $41.38   13.646%   $47.0267   $47.03   $47.05   $47.00  
  Purchase #4 $155.98   12.632%   $175.6834   $175.68   $175.70   $175.70  
  Purchase #5 $168.69   12.550%   $189.8606   $189.86   $189.85   $189.90  
  Purchase #6 $12.82   12.631%   $14.4393   $14.44   $14.45   $14.40  
  Purchase #7 $136.29   5.174%   $143.3416   $143.34   $143.35   $143.30  
  7 purchase totals = $762.70       $826.8696   $826.87   $826.90   $826.80