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 $246.37   5.776%   $260.6003   $260.60   $260.60   $260.60  
  Purchase #2 $26.86   10.147%   $29.5855   $29.59   $29.60   $29.60  
  Purchase #3 $189.80   7.277%   $203.6117   $203.61   $203.60   $203.60  
  Purchase #4 $171.61   5.261%   $180.6384   $180.64   $180.65   $180.60  
  Purchase #5 $208.54   9.747%   $228.8664   $228.87   $228.85   $228.90  
  Purchase #6 $64.81   4.369%   $67.6415   $67.64   $67.65   $67.60  
  Purchase #7 $187.63   4.357%   $195.805   $195.81   $195.80   $195.80  
  7 purchase totals = $1,095.62       $1,166.7488   $1,166.76   $1,166.75   $1,166.70