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 $225.66   3.712%   $234.0365   $234.04   $234.05   $234.00  
  Purchase #2 $219.37   10.323%   $242.0156   $242.02   $242.00   $242.00  
  Purchase #3 $149.91   4.495%   $156.6485   $156.65   $156.65   $156.60  
  Purchase #4 $195.34   7.306%   $209.6115   $209.61   $209.60   $209.60  
  Purchase #5 $178.88   9.723%   $196.2725   $196.27   $196.25   $196.30  
  Purchase #6 $128.26   4.669%   $134.2485   $134.25   $134.25   $134.20  
  Purchase #7 $181.69   3.641%   $188.3053   $188.31   $188.30   $188.30  
  7 purchase totals = $1,279.11       $1,361.1384   $1,361.15   $1,361.10   $1,361.00