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 $35.27   12.282%   $39.6019   $39.60   $39.60   $39.60  
  Purchase #2 $55.31   10.821%   $61.2951   $61.30   $61.30   $61.30  
  Purchase #3 $95.88   6.724%   $102.327   $102.33   $102.35   $102.30  
  Purchase #4 $153.68   4.130%   $160.027   $160.03   $160.05   $160.00  
  Purchase #5 $106.81   6.344%   $113.586   $113.59   $113.60   $113.60  
  Purchase #6 $209.50   3.693%   $217.2368   $217.24   $217.25   $217.20  
  Purchase #7 $191.76   12.824%   $216.3513   $216.35   $216.35   $216.40  
  7 purchase totals = $848.21       $910.4251   $910.44   $910.50   $910.40