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 $228.44   5.458%   $240.9083   $240.91   $240.90   $240.90  
  Purchase #2 $30.64   11.254%   $34.0882   $34.09   $34.10   $34.10  
  Purchase #3 $250.77   10.511%   $277.1284   $277.13   $277.15   $277.10  
  Purchase #4 $178.71   10.493%   $197.462   $197.46   $197.45   $197.50  
  Purchase #5 $25.52   7.560%   $27.4493   $27.45   $27.45   $27.40  
  Purchase #6 $67.91   6.259%   $72.1605   $72.16   $72.15   $72.20  
  Purchase #7 $41.75   7.190%   $44.7518   $44.75   $44.75   $44.80  
  7 purchase totals = $823.74       $893.9485   $893.95   $893.95   $894.00