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 $134.99   11.782%   $150.8945   $150.89   $150.90   $150.90  
  Purchase #2 $163.92   9.581%   $179.6252   $179.63   $179.65   $179.60  
  Purchase #3 $224.57   11.620%   $250.665   $250.67   $250.65   $250.70  
  Purchase #4 $65.41   3.336%   $67.5921   $67.59   $67.60   $67.60  
  Purchase #5 $226.37   11.637%   $252.7127   $252.71   $252.70   $252.70  
  Purchase #6 $121.64   3.679%   $126.1151   $126.12   $126.10   $126.10  
  Purchase #7 $24.45   5.215%   $25.7251   $25.73   $25.75   $25.70  
  7 purchase totals = $961.35       $1,053.3297   $1,053.34   $1,053.35   $1,053.30