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 $95.97   8.701%   $104.3203   $104.32   $104.30   $104.30  
  Purchase #2 $161.46   8.751%   $175.5894   $175.59   $175.60   $175.60  
  Purchase #3 $124.91   8.863%   $135.9808   $135.98   $136.00   $136.00  
  Purchase #4 $70.28   8.302%   $76.1146   $76.11   $76.10   $76.10  
  Purchase #5 $181.48   13.205%   $205.4444   $205.44   $205.45   $205.40  
  Purchase #6 $76.35   10.499%   $84.366   $84.37   $84.35   $84.40  
  Purchase #7 $172.88   6.700%   $184.463   $184.46   $184.45   $184.50  
  7 purchase totals = $883.33       $966.2785   $966.27   $966.25   $966.30