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 $62.42   11.453%   $69.569   $69.57   $69.55   $69.60  
  Purchase #2 $18.48   3.650%   $19.1545   $19.15   $19.15   $19.20  
  Purchase #3 $44.32   13.337%   $50.231   $50.23   $50.25   $50.20  
  Purchase #4 $192.57   9.797%   $211.4361   $211.44   $211.45   $211.40  
  Purchase #5 $173.26   10.807%   $191.9842   $191.98   $192.00   $192.00  
  Purchase #6 $37.41   5.140%   $39.3329   $39.33   $39.35   $39.30  
  Purchase #7 $32.91   10.401%   $36.333   $36.33   $36.35   $36.30  
  7 purchase totals = $561.37       $618.0407   $618.03   $618.10   $618.00