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 $232.68   11.149%   $258.6215   $258.62   $258.60   $258.60  
  Purchase #2 $208.96   13.641%   $237.4642   $237.46   $237.45   $237.50  
  Purchase #3 $43.70   13.262%   $49.4955   $49.50   $49.50   $49.50  
  Purchase #4 $239.63   9.375%   $262.0953   $262.10   $262.10   $262.10  
  Purchase #5 $28.44   10.538%   $31.437   $31.44   $31.45   $31.40  
  Purchase #6 $129.36   12.476%   $145.499   $145.50   $145.50   $145.50  
  Purchase #7 $65.51   7.546%   $70.4534   $70.45   $70.45   $70.50  
  7 purchase totals = $948.28       $1,055.0659   $1,055.07   $1,055.05   $1,055.10