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 $151.86   3.574%   $157.2875   $157.29   $157.30   $157.30  
  Purchase #2 $85.67   6.851%   $91.5393   $91.54   $91.55   $91.50  
  Purchase #3 $177.95   3.578%   $184.3171   $184.32   $184.30   $184.30  
  Purchase #4 $215.37   5.377%   $226.9504   $226.95   $226.95   $227.00  
  Purchase #5 $202.41   5.419%   $213.3786   $213.38   $213.40   $213.40  
  Purchase #6 $111.47   9.411%   $121.9604   $121.96   $121.95   $122.00  
  Purchase #7 $250.54   6.444%   $266.6848   $266.68   $266.70   $266.70  
  7 purchase totals = $1,195.27       $1,262.1181   $1,262.12   $1,262.15   $1,262.20