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 $194.30   8.814%   $211.4256   $211.43   $211.45   $211.40  
  Purchase #2 $232.69   6.299%   $247.3471   $247.35   $247.35   $247.30  
  Purchase #3 $153.53   5.417%   $161.8467   $161.85   $161.85   $161.80  
  Purchase #4 $182.40   8.755%   $198.3691   $198.37   $198.35   $198.40  
  Purchase #5 $28.82   11.133%   $32.0285   $32.03   $32.05   $32.00  
  Purchase #6 $165.25   4.358%   $172.4516   $172.45   $172.45   $172.50  
  Purchase #7 $27.64   11.262%   $30.7528   $30.75   $30.75   $30.80  
  7 purchase totals = $984.63       $1,054.2214   $1,054.23   $1,054.25   $1,054.20