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 $82.41   10.714%   $91.2394   $91.24   $91.25   $91.20  
  Purchase #2 $191.94   10.235%   $211.5851   $211.59   $211.60   $211.60  
  Purchase #3 $58.80   11.558%   $65.5961   $65.60   $65.60   $65.60  
  Purchase #4 $183.99   4.670%   $192.5823   $192.58   $192.60   $192.60  
  Purchase #5 $245.60   9.713%   $269.4551   $269.46   $269.45   $269.50  
  Purchase #6 $170.84   4.404%   $178.3638   $178.36   $178.35   $178.40  
  Purchase #7 $51.70   9.308%   $56.5122   $56.51   $56.50   $56.50  
  7 purchase totals = $985.28       $1,065.3340   $1,065.34   $1,065.35   $1,065.40