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 $72.31   3.233%   $74.6478   $74.65   $74.65   $74.60  
  Purchase #2 $162.61   3.127%   $167.6948   $167.69   $167.70   $167.70  
  Purchase #3 $41.61   4.554%   $43.5049   $43.50   $43.50   $43.50  
  Purchase #4 $235.68   7.535%   $253.4385   $253.44   $253.45   $253.40  
  Purchase #5 $195.37   7.299%   $209.6301   $209.63   $209.65   $209.60  
  Purchase #6 $208.57   12.475%   $234.5891   $234.59   $234.60   $234.60  
  Purchase #7 $101.50   7.214%   $108.8222   $108.82   $108.80   $108.80  
  7 purchase totals = $1,017.65       $1,092.3274   $1,092.32   $1,092.35   $1,092.20