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 $90.60   5.420%   $95.5105   $95.51   $95.50   $95.50  
  Purchase #2 $44.53   12.415%   $50.0584   $50.06   $50.05   $50.10  
  Purchase #3 $63.94   3.828%   $66.3876   $66.39   $66.40   $66.40  
  Purchase #4 $192.65   8.134%   $208.3202   $208.32   $208.30   $208.30  
  Purchase #5 $146.39   5.156%   $153.9379   $153.94   $153.95   $153.90  
  Purchase #6 $56.90   3.144%   $58.6889   $58.69   $58.70   $58.70  
  Purchase #7 $181.88   6.755%   $194.166   $194.17   $194.15   $194.20  
  7 purchase totals = $776.89       $827.0695   $827.08   $827.05   $827.10