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 $79.91   8.474%   $86.6816   $86.68   $86.70   $86.70  
  Purchase #2 $233.48   7.370%   $250.6875   $250.69   $250.70   $250.70  
  Purchase #3 $55.39   6.778%   $59.1443   $59.14   $59.15   $59.10  
  Purchase #4 $57.47   5.107%   $60.405   $60.41   $60.40   $60.40  
  Purchase #5 $191.96   5.187%   $201.917   $201.92   $201.90   $201.90  
  Purchase #6 $201.61   4.710%   $211.1058   $211.11   $211.10   $211.10  
  Purchase #7 $217.29   7.497%   $233.5802   $233.58   $233.60   $233.60  
  7 purchase totals = $1,037.11       $1,103.5214   $1,103.53   $1,103.55   $1,103.50