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 $246.82   8.748%   $268.4118   $268.41   $268.40   $268.40  
  Purchase #2 $167.45   11.177%   $186.1659   $186.17   $186.15   $186.20  
  Purchase #3 $126.32   3.296%   $130.4835   $130.48   $130.50   $130.50  
  Purchase #4 $150.64   8.806%   $163.9054   $163.91   $163.90   $163.90  
  Purchase #5 $231.33   5.107%   $243.144   $243.14   $243.15   $243.10  
  Purchase #6 $143.79   8.326%   $155.762   $155.76   $155.75   $155.80  
  Purchase #7 $31.86   11.280%   $35.4538   $35.45   $35.45   $35.50  
  7 purchase totals = $1,098.21       $1,183.3264   $1,183.32   $1,183.30   $1,183.40