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 $167.78   10.648%   $185.6452   $185.65   $185.65   $185.60  
  Purchase #2 $237.37   13.607%   $269.6689   $269.67   $269.65   $269.70  
  Purchase #3 $63.91   4.752%   $66.947   $66.95   $66.95   $66.90  
  Purchase #4 $130.94   8.567%   $142.1576   $142.16   $142.15   $142.20  
  Purchase #5 $175.41   10.738%   $194.2455   $194.25   $194.25   $194.20  
  Purchase #6 $203.77   11.289%   $226.7736   $226.77   $226.75   $226.80  
  Purchase #7 $56.32   10.361%   $62.1553   $62.16   $62.15   $62.20  
  7 purchase totals = $1,035.50       $1,147.5931   $1,147.61   $1,147.55   $1,147.60