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 $244.80   7.309%   $262.6924   $262.69   $262.70   $262.70  
  Purchase #2 $43.58   7.676%   $46.9252   $46.93   $46.95   $46.90  
  Purchase #3 $20.92   7.836%   $22.5593   $22.56   $22.55   $22.60  
  Purchase #4 $160.69   7.422%   $172.6164   $172.62   $172.60   $172.60  
  Purchase #5 $241.59   13.634%   $274.5284   $274.53   $274.55   $274.50  
  Purchase #6 $12.75   9.500%   $13.9613   $13.96   $13.95   $14.00  
  Purchase #7 $53.30   7.133%   $57.1019   $57.10   $57.10   $57.10  
  7 purchase totals = $777.63       $850.3849   $850.39   $850.40   $850.40