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 $250.92   6.741%   $267.8345   $267.83   $267.85   $267.80  
  Purchase #2 $77.90   4.202%   $81.1734   $81.17   $81.15   $81.20  
  Purchase #3 $53.50   6.233%   $56.8347   $56.83   $56.85   $56.80  
  Purchase #4 $96.31   5.870%   $101.9634   $101.96   $101.95   $102.00  
  Purchase #5 $140.26   10.520%   $155.0154   $155.02   $155.00   $155.00  
  Purchase #6 $56.51   10.334%   $62.3497   $62.35   $62.35   $62.30  
  Purchase #7 $200.57   5.805%   $212.2131   $212.21   $212.20   $212.20  
  7 purchase totals = $875.97       $937.3842   $937.37   $937.35   $937.30