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 $44.91   8.276%   $48.6268   $48.63   $48.65   $48.60  
  Purchase #2 $152.26   8.124%   $164.6296   $164.63   $164.65   $164.60  
  Purchase #3 $241.38   7.785%   $260.1714   $260.17   $260.15   $260.20  
  Purchase #4 $74.81   6.539%   $79.7018   $79.70   $79.70   $79.70  
  Purchase #5 $113.41   9.272%   $123.9254   $123.93   $123.95   $123.90  
  Purchase #6 $22.78   7.111%   $24.3999   $24.40   $24.40   $24.40  
  Purchase #7 $48.46   11.590%   $54.0765   $54.08   $54.10   $54.10  
  7 purchase totals = $698.01       $755.5314   $755.54   $755.60   $755.50