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 $168.43   4.831%   $176.5669   $176.57   $176.55   $176.60  
  Purchase #2 $54.27   4.284%   $56.5949   $56.59   $56.60   $56.60  
  Purchase #3 $155.60   6.786%   $166.159   $166.16   $166.15   $166.20  
  Purchase #4 $163.30   4.532%   $170.7008   $170.70   $170.70   $170.70  
  Purchase #5 $148.64   4.502%   $155.3318   $155.33   $155.35   $155.30  
  Purchase #6 $240.69   12.857%   $271.6355   $271.64   $271.65   $271.60  
  Purchase #7 $11.33   13.775%   $12.8907   $12.89   $12.90   $12.90  
  7 purchase totals = $942.26       $1,009.8796   $1,009.88   $1,009.90   $1,009.90