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 $215.77   8.527%   $234.1687   $234.17   $234.15   $234.20  
  Purchase #2 $223.74   5.780%   $236.6722   $236.67   $236.65   $236.70  
  Purchase #3 $73.53   8.796%   $79.9977   $80.00   $80.00   $80.00  
  Purchase #4 $248.97   11.654%   $277.985   $277.99   $278.00   $278.00  
  Purchase #5 $110.98   6.140%   $117.7942   $117.79   $117.80   $117.80  
  Purchase #6 $108.66   4.340%   $113.3758   $113.38   $113.40   $113.40  
  Purchase #7 $135.62   5.873%   $143.585   $143.59   $143.60   $143.60  
  7 purchase totals = $1,117.27       $1,203.5786   $1,203.59   $1,203.60   $1,203.70