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 $234.28   13.784%   $266.5732   $266.57   $266.55   $266.60  
  Purchase #2 $205.44   3.191%   $211.9956   $212.00   $212.00   $212.00  
  Purchase #3 $76.78   6.775%   $81.9818   $81.98   $82.00   $82.00  
  Purchase #4 $91.57   7.649%   $98.5742   $98.57   $98.55   $98.60  
  Purchase #5 $187.65   13.626%   $213.2192   $213.22   $213.20   $213.20  
  Purchase #6 $29.67   7.602%   $31.9255   $31.93   $31.95   $31.90  
  Purchase #7 $120.91   5.340%   $127.3666   $127.37   $127.35   $127.40  
  7 purchase totals = $946.30       $1,031.6361   $1,031.64   $1,031.60   $1,031.70