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 $163.55   10.109%   $180.0833   $180.08   $180.10   $180.10  
  Purchase #2 $25.87   8.180%   $27.9862   $27.99   $28.00   $28.00  
  Purchase #3 $100.71   7.816%   $108.5815   $108.58   $108.60   $108.60  
  Purchase #4 $76.67   9.748%   $84.1438   $84.14   $84.15   $84.10  
  Purchase #5 $137.30   12.231%   $154.0932   $154.09   $154.10   $154.10  
  Purchase #6 $24.83   5.162%   $26.1117   $26.11   $26.10   $26.10  
  Purchase #7 $162.47   3.577%   $168.2816   $168.28   $168.30   $168.30  
  7 purchase totals = $691.40       $749.2813   $749.27   $749.35   $749.30