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 $71.57   8.129%   $77.3879   $77.39   $77.40   $77.40  
  Purchase #2 $229.30   13.367%   $259.9505   $259.95   $259.95   $260.00  
  Purchase #3 $149.50   9.392%   $163.541   $163.54   $163.55   $163.50  
  Purchase #4 $130.38   4.687%   $136.4909   $136.49   $136.50   $136.50  
  Purchase #5 $115.62   13.671%   $131.4264   $131.43   $131.45   $131.40  
  Purchase #6 $209.98   11.338%   $233.7875   $233.79   $233.80   $233.80  
  Purchase #7 $62.94   4.604%   $65.8378   $65.84   $65.85   $65.80  
  7 purchase totals = $969.29       $1,068.4220   $1,068.43   $1,068.50   $1,068.40