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 $116.73   7.762%   $125.7906   $125.79   $125.80   $125.80  
  Purchase #2 $108.93   10.631%   $120.5103   $120.51   $120.50   $120.50  
  Purchase #3 $187.52   9.652%   $205.6194   $205.62   $205.60   $205.60  
  Purchase #4 $61.40   10.758%   $68.0054   $68.01   $68.00   $68.00  
  Purchase #5 $91.41   3.528%   $94.6349   $94.63   $94.65   $94.60  
  Purchase #6 $168.56   13.644%   $191.5583   $191.56   $191.55   $191.60  
  Purchase #7 $242.49   11.573%   $270.5534   $270.55   $270.55   $270.60  
  7 purchase totals = $977.04       $1,076.6723   $1,076.67   $1,076.65   $1,076.70