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 $208.29   12.810%   $234.9719   $234.97   $234.95   $235.00  
  Purchase #2 $214.96   9.155%   $234.6396   $234.64   $234.65   $234.60  
  Purchase #3 $44.80   10.582%   $49.5407   $49.54   $49.55   $49.50  
  Purchase #4 $131.37   10.596%   $145.29   $145.29   $145.30   $145.30  
  Purchase #5 $14.89   11.170%   $16.5532   $16.55   $16.55   $16.60  
  Purchase #6 $31.38   4.291%   $32.7265   $32.73   $32.75   $32.70  
  Purchase #7 $28.88   8.170%   $31.2395   $31.24   $31.25   $31.20  
  7 purchase totals = $674.57       $744.9614   $744.96   $745.00   $744.90