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 $87.44   6.706%   $93.3037   $93.30   $93.30   $93.30  
  Purchase #2 $111.45   13.191%   $126.1514   $126.15   $126.15   $126.20  
  Purchase #3 $128.37   11.793%   $143.5087   $143.51   $143.50   $143.50  
  Purchase #4 $24.34   13.435%   $27.6101   $27.61   $27.60   $27.60  
  Purchase #5 $8.86   8.359%   $9.6006   $9.60   $9.60   $9.60  
  Purchase #6 $61.83   8.289%   $66.9551   $66.96   $66.95   $67.00  
  Purchase #7 $229.85   5.148%   $241.6827   $241.68   $241.70   $241.70  
  7 purchase totals = $652.14       $708.8123   $708.81   $708.80   $708.90