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 $58.67   8.822%   $63.8459   $63.85   $63.85   $63.80  
  Purchase #2 $95.88   5.369%   $101.0278   $101.03   $101.05   $101.00  
  Purchase #3 $190.97   10.424%   $210.8767   $210.88   $210.90   $210.90  
  Purchase #4 $250.45   7.838%   $270.0803   $270.08   $270.10   $270.10  
  Purchase #5 $229.72   10.461%   $253.751   $253.75   $253.75   $253.80  
  Purchase #6 $87.64   7.860%   $94.5285   $94.53   $94.55   $94.50  
  Purchase #7 $68.70   12.140%   $77.0402   $77.04   $77.05   $77.00  
  7 purchase totals = $982.03       $1,071.1504   $1,071.16   $1,071.25   $1,071.10