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 $48.44   11.697%   $54.106   $54.11   $54.10   $54.10  
  Purchase #2 $184.32   13.542%   $209.2806   $209.28   $209.30   $209.30  
  Purchase #3 $96.96   5.777%   $102.5614   $102.56   $102.55   $102.60  
  Purchase #4 $65.76   6.285%   $69.893   $69.89   $69.90   $69.90  
  Purchase #5 $155.55   5.296%   $163.7879   $163.79   $163.80   $163.80  
  Purchase #6 $174.38   10.169%   $192.1127   $192.11   $192.10   $192.10  
  Purchase #7 $197.28   9.445%   $215.9131   $215.91   $215.90   $215.90  
  7 purchase totals = $922.69       $1,007.6547   $1,007.65   $1,007.65   $1,007.70