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 $55.78   12.371%   $62.6805   $62.68   $62.70   $62.70  
  Purchase #2 $134.35   8.408%   $145.6461   $145.65   $145.65   $145.60  
  Purchase #3 $168.57   7.461%   $181.147   $181.15   $181.15   $181.10  
  Purchase #4 $199.78   8.687%   $217.1349   $217.13   $217.15   $217.10  
  Purchase #5 $21.89   4.865%   $22.9549   $22.95   $22.95   $23.00  
  Purchase #6 $224.82   10.779%   $249.0533   $249.05   $249.05   $249.10  
  Purchase #7 $217.46   3.351%   $224.7471   $224.75   $224.75   $224.70  
  7 purchase totals = $1,022.65       $1,103.3638   $1,103.36   $1,103.40   $1,103.30