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 $61.58   7.365%   $66.1154   $66.12   $66.10   $66.10  
  Purchase #2 $237.65   12.208%   $266.6623   $266.66   $266.65   $266.70  
  Purchase #3 $99.68   10.495%   $110.1414   $110.14   $110.15   $110.10  
  Purchase #4 $222.39   13.363%   $252.108   $252.11   $252.10   $252.10  
  Purchase #5 $81.83   6.649%   $87.2709   $87.27   $87.25   $87.30  
  Purchase #6 $26.42   10.141%   $29.0993   $29.10   $29.10   $29.10  
  Purchase #7 $183.55   13.183%   $207.7474   $207.75   $207.75   $207.70  
  7 purchase totals = $913.10       $1,019.1447   $1,019.15   $1,019.10   $1,019.10