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 $56.41   11.356%   $62.8159   $62.82   $62.80   $62.80  
  Purchase #2 $201.81   12.822%   $227.6861   $227.69   $227.70   $227.70  
  Purchase #3 $109.29   10.553%   $120.8234   $120.82   $120.80   $120.80  
  Purchase #4 $208.37   4.568%   $217.8883   $217.89   $217.90   $217.90  
  Purchase #5 $153.56   13.231%   $173.8775   $173.88   $173.90   $173.90  
  Purchase #6 $85.75   7.553%   $92.2267   $92.23   $92.25   $92.20  
  Purchase #7 $249.62   9.799%   $274.0803   $274.08   $274.10   $274.10  
  7 purchase totals = $1,064.81       $1,169.3982   $1,169.41   $1,169.45   $1,169.40