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 $90.96   13.109%   $102.8839   $102.88   $102.90   $102.90  
  Purchase #2 $235.38   7.407%   $252.8146   $252.81   $252.80   $252.80  
  Purchase #3 $169.34   12.165%   $189.9402   $189.94   $189.95   $189.90  
  Purchase #4 $56.35   6.530%   $60.0297   $60.03   $60.05   $60.00  
  Purchase #5 $146.77   6.821%   $156.7812   $156.78   $156.80   $156.80  
  Purchase #6 $37.80   7.507%   $40.6376   $40.64   $40.65   $40.60  
  Purchase #7 $178.34   11.788%   $199.3627   $199.36   $199.35   $199.40  
  7 purchase totals = $914.94       $1,002.4499   $1,002.44   $1,002.50   $1,002.40