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 $57.28   10.239%   $63.1449   $63.14   $63.15   $63.10  
  Purchase #2 $125.54   7.499%   $134.9542   $134.95   $134.95   $135.00  
  Purchase #3 $44.50   10.648%   $49.2384   $49.24   $49.25   $49.20  
  Purchase #4 $245.86   11.417%   $273.9298   $273.93   $273.95   $273.90  
  Purchase #5 $235.41   12.817%   $265.5825   $265.58   $265.60   $265.60  
  Purchase #6 $236.39   6.103%   $250.8169   $250.82   $250.80   $250.80  
  Purchase #7 $161.46   12.593%   $181.7927   $181.79   $181.80   $181.80  
  7 purchase totals = $1,106.44       $1,219.4594   $1,219.45   $1,219.50   $1,219.40