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 $157.43   6.109%   $167.0474   $167.05   $167.05   $167.00  
  Purchase #2 $241.61   3.848%   $250.9072   $250.91   $250.90   $250.90  
  Purchase #3 $221.59   9.769%   $243.2371   $243.24   $243.25   $243.20  
  Purchase #4 $116.27   5.468%   $122.6276   $122.63   $122.65   $122.60  
  Purchase #5 $146.30   9.367%   $160.0039   $160.00   $160.00   $160.00  
  Purchase #6 $190.56   3.484%   $197.1991   $197.20   $197.20   $197.20  
  Purchase #7 $213.50   6.142%   $226.6132   $226.61   $226.60   $226.60  
  7 purchase totals = $1,287.26       $1,367.6355   $1,367.64   $1,367.65   $1,367.50