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 $235.27   8.237%   $254.6492   $254.65   $254.65   $254.60  
  Purchase #2 $157.39   9.369%   $172.1359   $172.14   $172.15   $172.10  
  Purchase #3 $223.78   4.308%   $233.4204   $233.42   $233.40   $233.40  
  Purchase #4 $163.26   10.800%   $180.8921   $180.89   $180.90   $180.90  
  Purchase #5 $23.40   4.378%   $24.4245   $24.42   $24.40   $24.40  
  Purchase #6 $131.53   13.422%   $149.184   $149.18   $149.20   $149.20  
  Purchase #7 $26.90   10.774%   $29.7982   $29.80   $29.80   $29.80  
  7 purchase totals = $961.53       $1,044.5043   $1,044.50   $1,044.50   $1,044.40