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 $52.74   7.359%   $56.6211   $56.62   $56.60   $56.60  
  Purchase #2 $141.98   8.844%   $154.5367   $154.54   $154.55   $154.50  
  Purchase #3 $232.79   3.216%   $240.2765   $240.28   $240.30   $240.30  
  Purchase #4 $135.33   13.281%   $153.3032   $153.30   $153.30   $153.30  
  Purchase #5 $244.43   10.250%   $269.4841   $269.48   $269.50   $269.50  
  Purchase #6 $106.28   5.372%   $111.9894   $111.99   $112.00   $112.00  
  Purchase #7 $181.58   8.735%   $197.441   $197.44   $197.45   $197.40  
  7 purchase totals = $1,095.13       $1,183.6520   $1,183.65   $1,183.70   $1,183.60