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 $117.60   7.398%   $126.3   $126.30   $126.30   $126.30  
  Purchase #2 $107.81   11.321%   $120.0152   $120.02   $120.00   $120.00  
  Purchase #3 $163.93   5.811%   $173.456   $173.46   $173.45   $173.50  
  Purchase #4 $213.48   10.128%   $235.1013   $235.10   $235.10   $235.10  
  Purchase #5 $138.77   6.626%   $147.9649   $147.96   $147.95   $148.00  
  Purchase #6 $32.88   3.776%   $34.1215   $34.12   $34.10   $34.10  
  Purchase #7 $126.44   5.189%   $133.001   $133.00   $133.00   $133.00  
  7 purchase totals = $900.91       $969.9599   $969.96   $969.90   $970.00