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 $213.41   9.818%   $234.3626   $234.36   $234.35   $234.40  
  Purchase #2 $143.56   5.187%   $151.0065   $151.01   $151.00   $151.00  
  Purchase #3 $154.27   5.425%   $162.6391   $162.64   $162.65   $162.60  
  Purchase #4 $60.67   9.126%   $66.2067   $66.21   $66.20   $66.20  
  Purchase #5 $139.25   12.700%   $156.9348   $156.93   $156.95   $156.90  
  Purchase #6 $169.88   9.690%   $186.3414   $186.34   $186.35   $186.30  
  Purchase #7 $244.84   3.608%   $253.6738   $253.67   $253.65   $253.70  
  7 purchase totals = $1,125.88       $1,211.1649   $1,211.16   $1,211.15   $1,211.10