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 $163.32   8.748%   $177.6072   $177.61   $177.60   $177.60  
  Purchase #2 $58.37   5.761%   $61.7327   $61.73   $61.75   $61.70  
  Purchase #3 $38.70   3.551%   $40.0742   $40.07   $40.05   $40.10  
  Purchase #4 $198.43   6.616%   $211.5581   $211.56   $211.55   $211.60  
  Purchase #5 $158.25   11.147%   $175.8901   $175.89   $175.90   $175.90  
  Purchase #6 $237.31   9.302%   $259.3846   $259.38   $259.40   $259.40  
  Purchase #7 $99.93   6.534%   $106.4594   $106.46   $106.45   $106.50  
  7 purchase totals = $954.31       $1,032.7063   $1,032.70   $1,032.70   $1,032.80