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 $49.82   10.267%   $54.935   $54.94   $54.95   $54.90  
  Purchase #2 $119.63   4.487%   $124.9978   $125.00   $125.00   $125.00  
  Purchase #3 $241.72   8.674%   $262.6868   $262.69   $262.70   $262.70  
  Purchase #4 $77.27   5.494%   $81.5152   $81.52   $81.50   $81.50  
  Purchase #5 $131.73   12.222%   $147.83   $147.83   $147.85   $147.80  
  Purchase #6 $161.70   3.121%   $166.7467   $166.75   $166.75   $166.70  
  Purchase #7 $200.28   3.247%   $206.7831   $206.78   $206.80   $206.80  
  7 purchase totals = $982.15       $1,045.4946   $1,045.51   $1,045.55   $1,045.40