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 $58.69   3.411%   $60.6919   $60.69   $60.70   $60.70  
  Purchase #2 $146.51   7.586%   $157.6242   $157.62   $157.60   $157.60  
  Purchase #3 $203.65   9.803%   $223.6138   $223.61   $223.60   $223.60  
  Purchase #4 $230.98   9.380%   $252.6459   $252.65   $252.65   $252.60  
  Purchase #5 $9.86   7.536%   $10.603   $10.60   $10.60   $10.60  
  Purchase #6 $79.79   4.370%   $83.2768   $83.28   $83.30   $83.30  
  Purchase #7 $162.78   8.288%   $176.2712   $176.27   $176.25   $176.30  
  7 purchase totals = $892.26       $964.7268   $964.72   $964.70   $964.70