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 $241.55   8.122%   $261.1687   $261.17   $261.15   $261.20  
  Purchase #2 $217.72   4.107%   $226.6618   $226.66   $226.65   $226.70  
  Purchase #3 $212.96   11.440%   $237.3226   $237.32   $237.30   $237.30  
  Purchase #4 $128.99   12.654%   $145.3124   $145.31   $145.30   $145.30  
  Purchase #5 $114.44   11.490%   $127.5892   $127.59   $127.60   $127.60  
  Purchase #6 $192.44   7.561%   $206.9904   $206.99   $207.00   $207.00  
  Purchase #7 $87.31   9.532%   $95.6324   $95.63   $95.65   $95.60  
  7 purchase totals = $1,195.41       $1,300.6775   $1,300.67   $1,300.65   $1,300.70