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 $107.92   9.252%   $117.9048   $117.90   $117.90   $117.90  
  Purchase #2 $244.53   6.754%   $261.0456   $261.05   $261.05   $261.00  
  Purchase #3 $118.27   6.181%   $125.5803   $125.58   $125.60   $125.60  
  Purchase #4 $155.56   6.647%   $165.9001   $165.90   $165.90   $165.90  
  Purchase #5 $131.66   8.786%   $143.2276   $143.23   $143.25   $143.20  
  Purchase #6 $116.57   3.373%   $120.5019   $120.50   $120.50   $120.50  
  Purchase #7 $114.35   5.198%   $120.2939   $120.29   $120.30   $120.30  
  7 purchase totals = $988.86       $1,054.4542   $1,054.45   $1,054.50   $1,054.40