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 $44.83   6.372%   $47.6866   $47.69   $47.70   $47.70  
  Purchase #2 $34.95   5.582%   $36.9009   $36.90   $36.90   $36.90  
  Purchase #3 $191.98   6.405%   $204.2763   $204.28   $204.30   $204.30  
  Purchase #4 $241.93   11.328%   $269.3358   $269.34   $269.35   $269.30  
  Purchase #5 $200.64   13.587%   $227.901   $227.90   $227.90   $227.90  
  Purchase #6 $13.52   9.835%   $14.8497   $14.85   $14.85   $14.80  
  Purchase #7 $113.51   3.629%   $117.6293   $117.63   $117.65   $117.60  
  7 purchase totals = $841.36       $918.5796   $918.59   $918.65   $918.50