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 $238.49   11.193%   $265.1842   $265.18   $265.20   $265.20  
  Purchase #2 $194.41   5.738%   $205.5652   $205.57   $205.55   $205.60  
  Purchase #3 $78.58   5.635%   $83.008   $83.01   $83.00   $83.00  
  Purchase #4 $186.75   3.180%   $192.6887   $192.69   $192.70   $192.70  
  Purchase #5 $106.33   12.133%   $119.231   $119.23   $119.25   $119.20  
  Purchase #6 $243.80   12.544%   $274.3823   $274.38   $274.40   $274.40  
  Purchase #7 $12.58   4.229%   $13.112   $13.11   $13.10   $13.10  
  7 purchase totals = $1,060.94       $1,153.1714   $1,153.17   $1,153.20   $1,153.20