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 $57.43   9.129%   $62.6728   $62.67   $62.65   $62.70  
  Purchase #2 $194.96   4.482%   $203.6981   $203.70   $203.70   $203.70  
  Purchase #3 $235.37   8.799%   $256.0802   $256.08   $256.10   $256.10  
  Purchase #4 $164.94   9.150%   $180.032   $180.03   $180.05   $180.00  
  Purchase #5 $157.65   8.518%   $171.0786   $171.08   $171.10   $171.10  
  Purchase #6 $199.25   4.495%   $208.2063   $208.21   $208.20   $208.20  
  Purchase #7 $50.87   11.292%   $56.6142   $56.61   $56.60   $56.60  
  7 purchase totals = $1,060.47       $1,138.3822   $1,138.38   $1,138.40   $1,138.40