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 $151.57   8.338%   $164.2079   $164.21   $164.20   $164.20  
  Purchase #2 $28.61   13.821%   $32.5642   $32.56   $32.55   $32.60  
  Purchase #3 $216.52   11.193%   $240.7551   $240.76   $240.75   $240.80  
  Purchase #4 $219.95   4.855%   $230.6286   $230.63   $230.65   $230.60  
  Purchase #5 $118.63   7.344%   $127.3422   $127.34   $127.35   $127.30  
  Purchase #6 $240.27   11.788%   $268.593   $268.59   $268.60   $268.60  
  Purchase #7 $181.36   9.205%   $198.0542   $198.05   $198.05   $198.10  
  7 purchase totals = $1,156.91       $1,262.1452   $1,262.14   $1,262.15   $1,262.20