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 $38.81   11.526%   $43.2832   $43.28   $43.30   $43.30  
  Purchase #2 $168.81   4.439%   $176.3035   $176.30   $176.30   $176.30  
  Purchase #3 $183.53   9.843%   $201.5949   $201.59   $201.60   $201.60  
  Purchase #4 $66.36   6.496%   $70.6707   $70.67   $70.65   $70.70  
  Purchase #5 $203.59   10.782%   $225.5411   $225.54   $225.55   $225.50  
  Purchase #6 $164.52   7.293%   $176.5184   $176.52   $176.50   $176.50  
  Purchase #7 $195.30   9.526%   $213.9043   $213.90   $213.90   $213.90  
  7 purchase totals = $1,020.92       $1,107.8161   $1,107.80   $1,107.80   $1,107.80