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 $160.87   3.792%   $166.9702   $166.97   $166.95   $167.00  
  Purchase #2 $193.89   6.454%   $206.4037   $206.40   $206.40   $206.40  
  Purchase #3 $143.82   7.331%   $154.3634   $154.36   $154.35   $154.40  
  Purchase #4 $66.37   11.292%   $73.8645   $73.86   $73.85   $73.90  
  Purchase #5 $56.57   6.869%   $60.4558   $60.46   $60.45   $60.50  
  Purchase #6 $33.58   9.751%   $36.8544   $36.85   $36.85   $36.90  
  Purchase #7 $70.44   9.550%   $77.167   $77.17   $77.15   $77.20  
  7 purchase totals = $725.54       $776.0790   $776.07   $776.00   $776.30