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 $153.63   8.297%   $166.3767   $166.38   $166.40   $166.40  
  Purchase #2 $87.73   6.458%   $93.3956   $93.40   $93.40   $93.40  
  Purchase #3 $190.52   4.524%   $199.1391   $199.14   $199.15   $199.10  
  Purchase #4 $230.78   7.551%   $248.2062   $248.21   $248.20   $248.20  
  Purchase #5 $245.55   5.339%   $258.6599   $258.66   $258.65   $258.70  
  Purchase #6 $34.70   8.135%   $37.5228   $37.52   $37.50   $37.50  
  Purchase #7 $48.75   3.507%   $50.4597   $50.46   $50.45   $50.50  
  7 purchase totals = $991.66       $1,053.7600   $1,053.77   $1,053.75   $1,053.80