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 $59.26   12.729%   $66.8032   $66.80   $66.80   $66.80  
  Purchase #2 $232.49   10.451%   $256.7875   $256.79   $256.80   $256.80  
  Purchase #3 $127.89   5.246%   $134.5991   $134.60   $134.60   $134.60  
  Purchase #4 $73.49   7.669%   $79.1259   $79.13   $79.15   $79.10  
  Purchase #5 $149.91   9.486%   $164.1305   $164.13   $164.15   $164.10  
  Purchase #6 $192.90   7.241%   $206.8679   $206.87   $206.85   $206.90  
  Purchase #7 $99.31   6.834%   $106.0968   $106.10   $106.10   $106.10  
  7 purchase totals = $935.25       $1,014.4109   $1,014.42   $1,014.45   $1,014.40