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 $226.84   9.307%   $247.952   $247.95   $247.95   $248.00  
  Purchase #2 $218.26   12.367%   $245.2522   $245.25   $245.25   $245.30  
  Purchase #3 $67.53   10.442%   $74.5815   $74.58   $74.60   $74.60  
  Purchase #4 $182.63   7.170%   $195.7246   $195.72   $195.70   $195.70  
  Purchase #5 $214.86   9.282%   $234.8033   $234.80   $234.80   $234.80  
  Purchase #6 $197.90   9.559%   $216.8173   $216.82   $216.80   $216.80  
  Purchase #7 $157.58   4.115%   $164.0644   $164.06   $164.05   $164.10  
  7 purchase totals = $1,265.60       $1,379.1953   $1,379.18   $1,379.15   $1,379.30