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 $63.85   11.450%   $71.1608   $71.16   $71.15   $71.20  
  Purchase #2 $24.94   6.155%   $26.4751   $26.48   $26.50   $26.50  
  Purchase #3 $177.54   4.159%   $184.9239   $184.92   $184.90   $184.90  
  Purchase #4 $149.70   7.872%   $161.4844   $161.48   $161.50   $161.50  
  Purchase #5 $60.80   12.271%   $68.2608   $68.26   $68.25   $68.30  
  Purchase #6 $249.54   13.236%   $282.5691   $282.57   $282.55   $282.60  
  Purchase #7 $249.90   10.313%   $275.6722   $275.67   $275.65   $275.70  
  7 purchase totals = $976.27       $1,070.5463   $1,070.54   $1,070.50   $1,070.70