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 $59.52   6.352%   $63.3007   $63.30   $63.30   $63.30  
  Purchase #2 $227.61   11.110%   $252.8975   $252.90   $252.90   $252.90  
  Purchase #3 $81.30   8.752%   $88.4154   $88.42   $88.40   $88.40  
  Purchase #4 $237.44   10.463%   $262.2833   $262.28   $262.30   $262.30  
  Purchase #5 $45.36   5.103%   $47.6747   $47.67   $47.65   $47.70  
  Purchase #6 $228.47   4.677%   $239.1555   $239.16   $239.15   $239.20  
  Purchase #7 $43.76   13.830%   $49.812   $49.81   $49.80   $49.80  
  7 purchase totals = $923.46       $1,003.5391   $1,003.54   $1,003.50   $1,003.60