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 $134.41   8.539%   $145.8873   $145.89   $145.90   $145.90  
  Purchase #2 $161.27   7.173%   $172.8379   $172.84   $172.85   $172.80  
  Purchase #3 $71.35   7.562%   $76.7455   $76.75   $76.75   $76.70  
  Purchase #4 $22.92   8.678%   $24.909   $24.91   $24.90   $24.90  
  Purchase #5 $126.83   7.615%   $136.4881   $136.49   $136.50   $136.50  
  Purchase #6 $221.28   11.561%   $246.8622   $246.86   $246.85   $246.90  
  Purchase #7 $56.40   7.325%   $60.5313   $60.53   $60.55   $60.50  
  7 purchase totals = $794.46       $864.2613   $864.27   $864.30   $864.20