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 $65.42   3.481%   $67.6973   $67.70   $67.70   $67.70  
  Purchase #2 $137.65   3.120%   $141.9447   $141.94   $141.95   $141.90  
  Purchase #3 $240.45   9.251%   $262.694   $262.69   $262.70   $262.70  
  Purchase #4 $59.65   6.397%   $63.4658   $63.47   $63.45   $63.50  
  Purchase #5 $74.33   11.457%   $82.846   $82.85   $82.85   $82.80  
  Purchase #6 $121.93   10.157%   $134.3144   $134.31   $134.30   $134.30  
  Purchase #7 $97.67   5.337%   $102.8826   $102.88   $102.90   $102.90  
  7 purchase totals = $797.10       $855.8448   $855.84   $855.85   $855.80