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 $23.49   12.608%   $26.4516   $26.45   $26.45   $26.50  
  Purchase #2 $136.83   7.356%   $146.8952   $146.90   $146.90   $146.90  
  Purchase #3 $246.64   11.505%   $275.0159   $275.02   $275.00   $275.00  
  Purchase #4 $134.56   12.857%   $151.8604   $151.86   $151.85   $151.90  
  Purchase #5 $25.33   10.650%   $28.0276   $28.03   $28.05   $28.00  
  Purchase #6 $122.54   4.350%   $127.8705   $127.87   $127.85   $127.90  
  Purchase #7 $62.81   12.594%   $70.7203   $70.72   $70.70   $70.70  
  7 purchase totals = $752.20       $826.8415   $826.85   $826.80   $826.90