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 $73.90   12.268%   $82.9661   $82.97   $82.95   $83.00  
  Purchase #2 $29.50   3.769%   $30.6119   $30.61   $30.60   $30.60  
  Purchase #3 $10.93   6.400%   $11.6295   $11.63   $11.65   $11.60  
  Purchase #4 $58.51   4.386%   $61.0762   $61.08   $61.10   $61.10  
  Purchase #5 $232.48   3.497%   $240.6098   $240.61   $240.60   $240.60  
  Purchase #6 $238.99   4.106%   $248.8029   $248.80   $248.80   $248.80  
  Purchase #7 $81.43   12.731%   $91.7969   $91.80   $91.80   $91.80  
  7 purchase totals = $725.74       $767.4933   $767.50   $767.50   $767.50