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 $220.76   13.561%   $250.6973   $250.70   $250.70   $250.70  
  Purchase #2 $206.88   13.417%   $234.6371   $234.64   $234.65   $234.60  
  Purchase #3 $39.25   3.842%   $40.758   $40.76   $40.75   $40.80  
  Purchase #4 $160.99   11.356%   $179.272   $179.27   $179.25   $179.30  
  Purchase #5 $215.46   7.356%   $231.3092   $231.31   $231.30   $231.30  
  Purchase #6 $46.28   7.758%   $49.8704   $49.87   $49.85   $49.90  
  Purchase #7 $36.49   5.489%   $38.4929   $38.49   $38.50   $38.50  
  7 purchase totals = $926.11       $1,025.0369   $1,025.04   $1,025.00   $1,025.10