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 $185.99   6.102%   $197.3391   $197.34   $197.35   $197.30  
  Purchase #2 $249.35   5.223%   $262.3736   $262.37   $262.35   $262.40  
  Purchase #3 $217.82   11.223%   $242.2659   $242.27   $242.25   $242.30  
  Purchase #4 $135.58   4.558%   $141.7597   $141.76   $141.75   $141.80  
  Purchase #5 $113.44   9.611%   $124.3427   $124.34   $124.35   $124.30  
  Purchase #6 $54.28   4.129%   $56.5212   $56.52   $56.50   $56.50  
  Purchase #7 $23.88   8.557%   $25.9234   $25.92   $25.90   $25.90  
  7 purchase totals = $980.34       $1,050.5256   $1,050.52   $1,050.45   $1,050.50