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 $75.97   10.213%   $83.7288   $83.73   $83.75   $83.70  
  Purchase #2 $234.60   9.439%   $256.7439   $256.74   $256.75   $256.70  
  Purchase #3 $241.48   4.638%   $252.6798   $252.68   $252.70   $252.70  
  Purchase #4 $168.59   9.169%   $184.048   $184.05   $184.05   $184.00  
  Purchase #5 $44.25   3.866%   $45.9607   $45.96   $45.95   $46.00  
  Purchase #6 $187.62   3.646%   $194.4606   $194.46   $194.45   $194.50  
  Purchase #7 $249.31   11.309%   $277.5045   $277.50   $277.50   $277.50  
  7 purchase totals = $1,201.82       $1,295.1263   $1,295.12   $1,295.15   $1,295.10