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 $22.51   6.727%   $24.0242   $24.02   $24.00   $24.00  
  Purchase #2 $225.34   5.108%   $236.8504   $236.85   $236.85   $236.90  
  Purchase #3 $42.54   4.843%   $44.6002   $44.60   $44.60   $44.60  
  Purchase #4 $118.47   13.171%   $134.0737   $134.07   $134.05   $134.10  
  Purchase #5 $212.87   7.237%   $228.2754   $228.28   $228.30   $228.30  
  Purchase #6 $223.46   5.475%   $235.6944   $235.69   $235.70   $235.70  
  Purchase #7 $246.96   4.479%   $258.0213   $258.02   $258.00   $258.00  
  7 purchase totals = $1,092.15       $1,161.5396   $1,161.53   $1,161.50   $1,161.60