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 $205.46   10.274%   $226.569   $226.57   $226.55   $226.60  
  Purchase #2 $61.85   8.644%   $67.1963   $67.20   $67.20   $67.20  
  Purchase #3 $241.69   10.291%   $266.5623   $266.56   $266.55   $266.60  
  Purchase #4 $65.85   7.498%   $70.7874   $70.79   $70.80   $70.80  
  Purchase #5 $222.29   6.165%   $235.9942   $235.99   $236.00   $236.00  
  Purchase #6 $117.35   4.448%   $122.5697   $122.57   $122.55   $122.60  
  Purchase #7 $218.62   4.597%   $228.67   $228.67   $228.65   $228.70  
  7 purchase totals = $1,133.11       $1,218.3489   $1,218.35   $1,218.30   $1,218.50