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 $206.55   13.680%   $234.806   $234.81   $234.80   $234.80  
  Purchase #2 $80.53   9.851%   $88.463   $88.46   $88.45   $88.50  
  Purchase #3 $26.34   3.559%   $27.2774   $27.28   $27.30   $27.30  
  Purchase #4 $212.99   13.384%   $241.4966   $241.50   $241.50   $241.50  
  Purchase #5 $167.52   7.695%   $180.4107   $180.41   $180.40   $180.40  
  Purchase #6 $130.49   10.708%   $144.4629   $144.46   $144.45   $144.50  
  Purchase #7 $235.92   5.795%   $249.5916   $249.59   $249.60   $249.60  
  7 purchase totals = $1,060.34       $1,166.5082   $1,166.51   $1,166.50   $1,166.60