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 $206.52   3.752%   $214.2686   $214.27   $214.25   $214.30  
  Purchase #2 $83.77   4.405%   $87.4601   $87.46   $87.45   $87.50  
  Purchase #3 $95.25   11.793%   $106.4828   $106.48   $106.50   $106.50  
  Purchase #4 $104.64   10.397%   $115.5194   $115.52   $115.50   $115.50  
  Purchase #5 $166.45   12.316%   $186.95   $186.95   $186.95   $187.00  
  Purchase #6 $205.45   4.364%   $214.4158   $214.42   $214.40   $214.40  
  Purchase #7 $119.89   4.576%   $125.3762   $125.38   $125.40   $125.40  
  7 purchase totals = $981.97       $1,050.4729   $1,050.48   $1,050.45   $1,050.60