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 $57.27   11.591%   $63.9082   $63.91   $63.90   $63.90  
  Purchase #2 $97.84   13.132%   $110.6883   $110.69   $110.70   $110.70  
  Purchase #3 $239.44   7.771%   $258.0469   $258.05   $258.05   $258.00  
  Purchase #4 $147.33   9.193%   $160.874   $160.87   $160.85   $160.90  
  Purchase #5 $90.90   12.124%   $101.9207   $101.92   $101.90   $101.90  
  Purchase #6 $232.45   3.128%   $239.721   $239.72   $239.70   $239.70  
  Purchase #7 $149.91   5.122%   $157.5884   $157.59   $157.60   $157.60  
  7 purchase totals = $1,015.14       $1,092.7475   $1,092.75   $1,092.70   $1,092.70