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 $187.67   7.397%   $201.5519   $201.55   $201.55   $201.60  
  Purchase #2 $53.84   4.304%   $56.1573   $56.16   $56.15   $56.20  
  Purchase #3 $184.64   5.321%   $194.4647   $194.46   $194.45   $194.50  
  Purchase #4 $57.88   11.412%   $64.4853   $64.49   $64.50   $64.50  
  Purchase #5 $56.71   8.523%   $61.5434   $61.54   $61.55   $61.50  
  Purchase #6 $60.65   5.541%   $64.0106   $64.01   $64.00   $64.00  
  Purchase #7 $114.56   6.668%   $122.1989   $122.20   $122.20   $122.20  
  7 purchase totals = $715.95       $764.4121   $764.41   $764.40   $764.50