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 $56.95   11.289%   $63.3791   $63.38   $63.40   $63.40  
  Purchase #2 $86.51   13.811%   $98.4579   $98.46   $98.45   $98.50  
  Purchase #3 $202.41   4.444%   $211.4051   $211.41   $211.40   $211.40  
  Purchase #4 $61.86   8.433%   $67.0767   $67.08   $67.10   $67.10  
  Purchase #5 $210.42   12.752%   $237.2528   $237.25   $237.25   $237.30  
  Purchase #6 $227.58   9.401%   $248.9748   $248.97   $248.95   $249.00  
  Purchase #7 $158.52   6.690%   $169.125   $169.13   $169.15   $169.10  
  7 purchase totals = $1,004.25       $1,095.6714   $1,095.68   $1,095.70   $1,095.80