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 $223.29   9.658%   $244.8553   $244.86   $244.85   $244.90  
  Purchase #2 $156.43   11.136%   $173.85   $173.85   $173.85   $173.90  
  Purchase #3 $177.79   8.634%   $193.1404   $193.14   $193.15   $193.10  
  Purchase #4 $136.90   7.217%   $146.7801   $146.78   $146.80   $146.80  
  Purchase #5 $71.27   12.641%   $80.2792   $80.28   $80.30   $80.30  
  Purchase #6 $5.62   4.833%   $5.8916   $5.89   $5.90   $5.90  
  Purchase #7 $217.26   6.260%   $230.8605   $230.86   $230.85   $230.90  
  7 purchase totals = $988.56       $1,075.6571   $1,075.66   $1,075.70   $1,075.80