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 $235.27   11.757%   $262.9307   $262.93   $262.95   $262.90  
  Purchase #2 $238.52   6.439%   $253.8783   $253.88   $253.90   $253.90  
  Purchase #3 $241.47   8.646%   $262.3475   $262.35   $262.35   $262.30  
  Purchase #4 $39.26   12.862%   $44.3096   $44.31   $44.30   $44.30  
  Purchase #5 $49.48   13.165%   $55.994   $55.99   $56.00   $56.00  
  Purchase #6 $233.99   5.409%   $246.6465   $246.65   $246.65   $246.60  
  Purchase #7 $43.95   4.433%   $45.8983   $45.90   $45.90   $45.90  
  7 purchase totals = $1,081.94       $1,172.0049   $1,172.01   $1,172.05   $1,171.90