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 $46.94   12.300%   $52.7136   $52.71   $52.70   $52.70  
  Purchase #2 $77.45   6.303%   $82.3317   $82.33   $82.35   $82.30  
  Purchase #3 $60.84   10.173%   $67.0293   $67.03   $67.05   $67.00  
  Purchase #4 $183.58   5.165%   $193.0619   $193.06   $193.05   $193.10  
  Purchase #5 $160.97   9.398%   $176.098   $176.10   $176.10   $176.10  
  Purchase #6 $212.33   4.322%   $221.5069   $221.51   $221.50   $221.50  
  Purchase #7 $27.39   9.531%   $30.0005   $30.00   $30.00   $30.00  
  7 purchase totals = $769.50       $822.7419   $822.74   $822.75   $822.70