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 $133.51   13.622%   $151.6967   $151.70   $151.70   $151.70  
  Purchase #2 $172.92   10.513%   $191.0991   $191.10   $191.10   $191.10  
  Purchase #3 $163.80   6.830%   $174.9875   $174.99   $175.00   $175.00  
  Purchase #4 $53.41   12.513%   $60.0932   $60.09   $60.10   $60.10  
  Purchase #5 $149.77   4.486%   $156.4887   $156.49   $156.50   $156.50  
  Purchase #6 $157.87   9.181%   $172.364   $172.36   $172.35   $172.40  
  Purchase #7 $240.42   4.137%   $250.3662   $250.37   $250.35   $250.40  
  7 purchase totals = $1,071.70       $1,157.0954   $1,157.10   $1,157.10   $1,157.20