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 $50.69   3.185%   $52.3045   $52.30   $52.30   $52.30  
  Purchase #2 $49.56   13.485%   $56.2432   $56.24   $56.25   $56.20  
  Purchase #3 $60.74   11.562%   $67.7628   $67.76   $67.75   $67.80  
  Purchase #4 $246.45   5.585%   $260.2142   $260.21   $260.20   $260.20  
  Purchase #5 $161.84   7.594%   $174.1301   $174.13   $174.15   $174.10  
  Purchase #6 $190.43   4.316%   $198.649   $198.65   $198.65   $198.60  
  Purchase #7 $9.58   13.212%   $10.8457   $10.85   $10.85   $10.80  
  7 purchase totals = $769.29       $820.1495   $820.14   $820.15   $820.00