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 $141.54   10.731%   $156.7287   $156.73   $156.75   $156.70  
  Purchase #2 $229.63   13.568%   $260.7862   $260.79   $260.80   $260.80  
  Purchase #3 $208.93   12.526%   $235.1006   $235.10   $235.10   $235.10  
  Purchase #4 $24.67   6.474%   $26.2671   $26.27   $26.25   $26.30  
  Purchase #5 $134.61   3.250%   $138.9848   $138.98   $139.00   $139.00  
  Purchase #6 $231.57   10.151%   $255.0767   $255.08   $255.10   $255.10  
  Purchase #7 $151.67   10.586%   $167.7258   $167.73   $167.75   $167.70  
  7 purchase totals = $1,122.62       $1,240.6699   $1,240.68   $1,240.75   $1,240.70