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 $23.28   4.241%   $24.2673   $24.27   $24.25   $24.30  
  Purchase #2 $187.91   13.324%   $212.9471   $212.95   $212.95   $212.90  
  Purchase #3 $102.72   11.655%   $114.692   $114.69   $114.70   $114.70  
  Purchase #4 $13.47   6.228%   $14.3089   $14.31   $14.30   $14.30  
  Purchase #5 $108.65   3.803%   $112.782   $112.78   $112.80   $112.80  
  Purchase #6 $45.63   9.582%   $50.0023   $50.00   $50.00   $50.00  
  Purchase #7 $87.43   3.235%   $90.2584   $90.26   $90.25   $90.30  
  7 purchase totals = $569.09       $619.2580   $619.26   $619.25   $619.30