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 $68.67   8.396%   $74.4355   $74.44   $74.45   $74.40  
  Purchase #2 $154.36   7.550%   $166.0142   $166.01   $166.00   $166.00  
  Purchase #3 $21.76   11.631%   $24.2909   $24.29   $24.30   $24.30  
  Purchase #4 $48.87   7.616%   $52.5919   $52.59   $52.60   $52.60  
  Purchase #5 $205.47   6.789%   $219.4194   $219.42   $219.40   $219.40  
  Purchase #6 $211.45   10.750%   $234.1809   $234.18   $234.20   $234.20  
  Purchase #7 $60.29   5.743%   $63.7525   $63.75   $63.75   $63.80  
  7 purchase totals = $770.87       $834.6853   $834.68   $834.70   $834.70