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 $125.94   13.739%   $143.2429   $143.24   $143.25   $143.20  
  Purchase #2 $154.85   13.605%   $175.9173   $175.92   $175.90   $175.90  
  Purchase #3 $39.25   9.655%   $43.0396   $43.04   $43.05   $43.00  
  Purchase #4 $236.99   13.747%   $269.569   $269.57   $269.55   $269.60  
  Purchase #5 $123.85   13.847%   $140.9995   $141.00   $141.00   $141.00  
  Purchase #6 $184.33   10.307%   $203.3289   $203.33   $203.35   $203.30  
  Purchase #7 $52.66   12.517%   $59.2515   $59.25   $59.25   $59.30  
  7 purchase totals = $917.87       $1,035.3487   $1,035.35   $1,035.35   $1,035.30