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 $153.99   8.658%   $167.3225   $167.32   $167.30   $167.30  
  Purchase #2 $164.68   11.754%   $184.0365   $184.04   $184.05   $184.00  
  Purchase #3 $174.81   9.190%   $190.875   $190.88   $190.90   $190.90  
  Purchase #4 $40.67   5.771%   $43.0171   $43.02   $43.00   $43.00  
  Purchase #5 $70.44   5.662%   $74.4283   $74.43   $74.45   $74.40  
  Purchase #6 $186.77   4.414%   $195.014   $195.01   $195.00   $195.00  
  Purchase #7 $180.42   4.598%   $188.7157   $188.72   $188.70   $188.70  
  7 purchase totals = $971.78       $1,043.4091   $1,043.42   $1,043.40   $1,043.30