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 $204.99   7.780%   $220.9382   $220.94   $220.95   $220.90  
  Purchase #2 $114.35   12.274%   $128.3853   $128.39   $128.40   $128.40  
  Purchase #3 $53.82   4.520%   $56.2527   $56.25   $56.25   $56.30  
  Purchase #4 $49.34   9.550%   $54.052   $54.05   $54.05   $54.10  
  Purchase #5 $250.88   7.358%   $269.3398   $269.34   $269.35   $269.30  
  Purchase #6 $247.27   4.150%   $257.5317   $257.53   $257.55   $257.50  
  Purchase #7 $132.48   4.686%   $138.688   $138.69   $138.70   $138.70  
  7 purchase totals = $1,053.13       $1,125.1877   $1,125.19   $1,125.25   $1,125.20