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 $8.54   5.782%   $9.0338   $9.03   $9.05   $9.00  
  Purchase #2 $137.74   5.719%   $145.6174   $145.62   $145.60   $145.60  
  Purchase #3 $172.85   7.109%   $185.1379   $185.14   $185.15   $185.10  
  Purchase #4 $215.81   12.151%   $242.0331   $242.03   $242.05   $242.00  
  Purchase #5 $80.29   9.208%   $87.6831   $87.68   $87.70   $87.70  
  Purchase #6 $64.88   5.401%   $68.3842   $68.38   $68.40   $68.40  
  Purchase #7 $85.46   6.224%   $90.779   $90.78   $90.80   $90.80  
  7 purchase totals = $765.57       $828.6685   $828.66   $828.75   $828.60