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 $223.59   7.789%   $241.0054   $241.01   $241.00   $241.00  
  Purchase #2 $211.67   10.663%   $234.2404   $234.24   $234.25   $234.20  
  Purchase #3 $16.65   7.682%   $17.9291   $17.93   $17.95   $17.90  
  Purchase #4 $235.34   7.681%   $253.4165   $253.42   $253.40   $253.40  
  Purchase #5 $239.53   4.820%   $251.0753   $251.08   $251.10   $251.10  
  Purchase #6 $185.67   12.203%   $208.3273   $208.33   $208.35   $208.30  
  Purchase #7 $239.75   4.356%   $250.1935   $250.19   $250.20   $250.20  
  7 purchase totals = $1,352.20       $1,456.1875   $1,456.20   $1,456.25   $1,456.10