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 $147.84   4.832%   $154.9836   $154.98   $155.00   $155.00  
  Purchase #2 $32.87   6.642%   $35.0532   $35.05   $35.05   $35.10  
  Purchase #3 $210.44   13.862%   $239.6112   $239.61   $239.60   $239.60  
  Purchase #4 $244.34   9.532%   $267.6305   $267.63   $267.65   $267.60  
  Purchase #5 $192.51   4.339%   $200.863   $200.86   $200.85   $200.90  
  Purchase #6 $186.55   5.598%   $196.9931   $196.99   $197.00   $197.00  
  Purchase #7 $38.90   12.688%   $43.8356   $43.84   $43.85   $43.80  
  7 purchase totals = $1,053.45       $1,138.9702   $1,138.96   $1,139.00   $1,139.00