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 $56.48   3.303%   $58.3455   $58.35   $58.35   $58.30  
  Purchase #2 $97.72   8.394%   $105.9226   $105.92   $105.90   $105.90  
  Purchase #3 $206.85   10.202%   $227.9528   $227.95   $227.95   $228.00  
  Purchase #4 $202.54   12.237%   $227.3248   $227.32   $227.30   $227.30  
  Purchase #5 $242.26   13.277%   $274.4249   $274.42   $274.40   $274.40  
  Purchase #6 $52.79   7.136%   $56.5571   $56.56   $56.55   $56.60  
  Purchase #7 $41.31   11.199%   $45.9363   $45.94   $45.95   $45.90  
  7 purchase totals = $899.95       $996.4640   $996.46   $996.40   $996.40