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 $9.37   4.526%   $9.7941   $9.79   $9.80   $9.80  
  Purchase #2 $134.30   7.543%   $144.4302   $144.43   $144.45   $144.40  
  Purchase #3 $52.89   10.120%   $58.2425   $58.24   $58.25   $58.20  
  Purchase #4 $64.95   11.172%   $72.2062   $72.21   $72.20   $72.20  
  Purchase #5 $6.48   3.597%   $6.7131   $6.71   $6.70   $6.70  
  Purchase #6 $48.53   13.255%   $54.9627   $54.96   $54.95   $55.00  
  Purchase #7 $79.31   7.291%   $85.0925   $85.09   $85.10   $85.10  
  7 purchase totals = $395.83       $431.4413   $431.43   $431.45   $431.40