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 $185.96   10.573%   $205.6216   $205.62   $205.60   $205.60  
  Purchase #2 $97.48   11.790%   $108.9729   $108.97   $108.95   $109.00  
  Purchase #3 $236.62   5.768%   $250.2682   $250.27   $250.25   $250.30  
  Purchase #4 $73.32   8.596%   $79.6226   $79.62   $79.60   $79.60  
  Purchase #5 $222.59   5.281%   $234.345   $234.35   $234.35   $234.30  
  Purchase #6 $196.76   11.699%   $219.779   $219.78   $219.80   $219.80  
  Purchase #7 $84.84   12.511%   $95.4543   $95.45   $95.45   $95.50  
  7 purchase totals = $1,097.57       $1,194.0636   $1,194.06   $1,194.00   $1,194.10