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 $67.45   13.769%   $76.7372   $76.74   $76.75   $76.70  
  Purchase #2 $160.78   8.812%   $174.9479   $174.95   $174.95   $174.90  
  Purchase #3 $109.93   3.440%   $113.7116   $113.71   $113.70   $113.70  
  Purchase #4 $238.35   10.212%   $262.6903   $262.69   $262.70   $262.70  
  Purchase #5 $168.66   3.310%   $174.2426   $174.24   $174.25   $174.20  
  Purchase #6 $104.31   8.831%   $113.5216   $113.52   $113.50   $113.50  
  Purchase #7 $121.49   13.138%   $137.4514   $137.45   $137.45   $137.50  
  7 purchase totals = $970.97       $1,053.3026   $1,053.30   $1,053.30   $1,053.20