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 $24.86   3.732%   $25.7878   $25.79   $25.80   $25.80  
  Purchase #2 $112.44   12.294%   $126.2634   $126.26   $126.25   $126.30  
  Purchase #3 $125.70   3.202%   $129.7249   $129.72   $129.70   $129.70  
  Purchase #4 $96.57   11.390%   $107.5693   $107.57   $107.55   $107.60  
  Purchase #5 $56.31   4.492%   $58.8394   $58.84   $58.85   $58.80  
  Purchase #6 $111.61   12.617%   $125.6918   $125.69   $125.70   $125.70  
  Purchase #7 $229.52   5.325%   $241.7419   $241.74   $241.75   $241.70  
  7 purchase totals = $757.01       $815.6185   $815.61   $815.60   $815.60