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 $67.35   4.818%   $70.5949   $70.59   $70.60   $70.60  
  Purchase #2 $45.59   7.450%   $48.9865   $48.99   $49.00   $49.00  
  Purchase #3 $60.25   11.765%   $67.3384   $67.34   $67.35   $67.30  
  Purchase #4 $231.51   4.550%   $242.0437   $242.04   $242.05   $242.00  
  Purchase #5 $232.62   12.861%   $262.5373   $262.54   $262.55   $262.50  
  Purchase #6 $211.60   10.451%   $233.7143   $233.71   $233.70   $233.70  
  Purchase #7 $11.51   7.576%   $12.382   $12.38   $12.40   $12.40  
  7 purchase totals = $860.43       $937.5971   $937.59   $937.65   $937.50