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 $57.42   9.654%   $62.9633   $62.96   $62.95   $63.00  
  Purchase #2 $138.75   13.417%   $157.3661   $157.37   $157.35   $157.40  
  Purchase #3 $206.94   12.296%   $232.3853   $232.39   $232.40   $232.40  
  Purchase #4 $152.47   10.762%   $168.8788   $168.88   $168.90   $168.90  
  Purchase #5 $208.81   11.330%   $232.4682   $232.47   $232.45   $232.50  
  Purchase #6 $90.51   8.345%   $98.0631   $98.06   $98.05   $98.10  
  Purchase #7 $88.28   6.122%   $93.6845   $93.68   $93.70   $93.70  
  7 purchase totals = $943.18       $1,045.8093   $1,045.81   $1,045.80   $1,046.00