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 $162.76   11.396%   $181.3081   $181.31   $181.30   $181.30  
  Purchase #2 $223.50   10.499%   $246.9653   $246.97   $246.95   $247.00  
  Purchase #3 $229.50   4.512%   $239.855   $239.86   $239.85   $239.90  
  Purchase #4 $66.27   7.406%   $71.178   $71.18   $71.20   $71.20  
  Purchase #5 $18.66   3.743%   $19.3584   $19.36   $19.35   $19.40  
  Purchase #6 $164.39   11.537%   $183.3557   $183.36   $183.35   $183.40  
  Purchase #7 $77.97   3.593%   $80.7715   $80.77   $80.75   $80.80  
  7 purchase totals = $943.05       $1,022.7920   $1,022.81   $1,022.75   $1,023.00