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 $119.60   4.114%   $124.5203   $124.52   $124.50   $124.50  
  Purchase #2 $145.88   12.382%   $163.9429   $163.94   $163.95   $163.90  
  Purchase #3 $35.95   11.783%   $40.186   $40.19   $40.20   $40.20  
  Purchase #4 $241.61   5.834%   $255.7055   $255.71   $255.70   $255.70  
  Purchase #5 $239.37   9.549%   $262.2274   $262.23   $262.25   $262.20  
  Purchase #6 $77.31   12.651%   $87.0905   $87.09   $87.10   $87.10  
  Purchase #7 $154.37   4.235%   $160.9076   $160.91   $160.90   $160.90  
  7 purchase totals = $1,014.09       $1,094.5802   $1,094.59   $1,094.60   $1,094.50