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 $196.67   11.691%   $219.6627   $219.66   $219.65   $219.70  
  Purchase #2 $126.79   3.327%   $131.0083   $131.01   $131.00   $131.00  
  Purchase #3 $10.35   9.361%   $11.3189   $11.32   $11.30   $11.30  
  Purchase #4 $225.77   11.551%   $251.8487   $251.85   $251.85   $251.80  
  Purchase #5 $163.60   11.253%   $182.0099   $182.01   $182.00   $182.00  
  Purchase #6 $218.70   7.223%   $234.4967   $234.50   $234.50   $234.50  
  Purchase #7 $240.66   10.531%   $266.0039   $266.00   $266.00   $266.00  
  7 purchase totals = $1,182.54       $1,296.3491   $1,296.35   $1,296.30   $1,296.30